River Rock Calculator – How Much River Rock Do You Actually Need?
Enter your area and depth, and get the honest shopping list: cubic yards and cubic feet, litres and cubic metres, bag counts for any bag size, and a weight range you can plan a truck around — never a made-up exact weight.
Your area and depth
Advanced options — metric units, custom bag size and rock density
Advanced settings are already included in the result with their default values — open Advanced options to change them.
The 2,400–2,900 lb per cubic yard range is a typical published range for washed river rock. Wet rock runs heavier, and stone size changes the voids — if your supplier quotes a density, type it in and the weight range follows.
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What to order
Key Takeaways
- Volume is area × depth: 100 sq ft at 3 in needs 25.00 cu ft, or 0.93 cu yd.
- Bags always round up — 33.33 exact bags becomes 34 bags.
- Weight follows the 2,400–2,900 lb per cubic yard density range; wet rock runs heavier.
Contents
Depth changes the order fast
Same 100 sq ft, four depths. Doubling the depth doubles the rock — there is no bulk discount on volume.
| Depth | Cubic feet | Cubic yards | 0.5 cu ft bags |
|---|---|---|---|
| 2 in | 16.67 | 0.62 | 34 |
| 3 in | 25.00 | 0.93 | 50 |
| 4 in | 33.33 | 1.23 | 67 |
| 6 in | 50.00 | 1.85 | 100 |
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How it works
How the volume is worked out
Volume in cubic feet is area in square feet times depth in feet. Depth in inches is divided by 12 first: 100 sq ft at 3 inches is 100 times 0.25, which is 25 cubic feet. Cubic yards divide by 27, because one cubic yard is 3 feet by 3 feet by 3 feet. Litres multiply cubic feet by 28.3168, and cubic metres multiply by 0.0283168.
Bag counts divide the volume by the bag size and round up — you cannot buy part of a bag, so 12.5 bags becomes 13. The weight range multiplies the cubic yards by the low and high density you entered. A single exact weight would be dishonest: the same load weighs more after rain and less when it is dry, and larger stone leaves more air between pieces.
Questions, answered
Because river rock is sold loose, not weighed dry in a lab. Moisture, stone size and how tightly it is packed all move the weight. A range you can plan a truck around beats a precise-looking number that is wrong.
3 inches is the usual answer for garden paths and beds over landscape fabric. Go to 4 inches on slopes, where rock migrates downhill, and on drainage strips, where you want water to keep moving through the stone.
How the volume is worked out: area times depth, nothing else
The calculator’s method is one multiplication followed by two unit conversions, and every figure on the page can be checked from it. Volume in cubic feet equals area in square feet times depth in inches, divided by 12, because depth in inches must become depth in feet before it multiplies an area in square feet. The default case is 100 square feet at 3 inches deep, which gives 100 times 3 divided by 12, or 25.00 cubic feet. Dividing by 27, the number of cubic feet in a cubic yard, gives 0.93 cubic yards, and the page also shows the same volume as 707.92 litres and 0.71 cubic metres, so that whichever unit your supplier quotes, you have it without converting by hand.
Depth is the input that surprises people, because it changes the order far faster than area does in practice. Doubling the depth doubles the rock, exactly, with no bulk discount on volume. The default 100 square feet at 3 inches needs 25.00 cubic feet; at 2 inches it needs 16.67 cubic feet, and at 6 inches it needs 50.00 cubic feet. That is why the page’s own depth table is worth studying before you order: a path that was planned at 2 inches and then dug or edged to 4 inches does not need a little more rock, it needs twice as much. If your ground is uneven, measure the depth in several places and plan on the deeper readings, because the shallow spots do not cancel out the deep ones: volume follows the average depth across the whole area, and a dip that is twice as deep over a tenth of the area still adds a fifth to the total.
| Depth at 100 sq ft | Cubic feet | Cubic yards | 0.5 cu ft bags | Coverage per cubic yard |
|---|---|---|---|---|
| 1 in | 8.33 | 0.31 | 17 | 324.00 sq ft |
| 2 in | 16.67 | 0.62 | 34 | 162.00 sq ft |
| 3 in | 25.00 | 0.93 | 50 | 108.00 sq ft |
| 4 in | 33.33 | 1.23 | 67 | 81.00 sq ft |
| 5 in | 41.67 | 1.54 | 84 | 64.80 sq ft |
| 6 in | 50.00 | 1.85 | 100 | 54.00 sq ft |
The table above is the page’s own arithmetic at 100 square feet, and the rows the calculator itself displays confirm the pattern: 2 inches gives 16.67 cubic feet and 34 bags, 3 inches gives 25.00 cubic feet and 50 bags, 4 inches gives 33.33 cubic feet and 67 bags, and 6 inches gives 50.00 cubic feet and 100 bags. The 1-inch and 5-inch rows follow the same rule by arithmetic: 100 times 1 divided by 12 is 8.33 cubic feet, which is 0.31 cubic yards and 17 bags after rounding up, and 100 times 5 divided by 12 is 41.67 cubic feet, which is 1.54 cubic yards and 84 bags after rounding up. Coverage per cubic yard falls as depth rises, because one cubic yard spread thicker covers less ground: at 2 inches it covers 162.00 square feet, at 3 inches 108.00, at 4 inches 81.00, and at 6 inches 54.00. Those coverage figures are the same division seen from the other side, and they are useful when a supplier quotes by the yard rather than by the bag.
Area works the same linear way, which makes irregular shapes manageable. A rectangle’s area is length times width, and an irregular bed can be split into rectangles whose areas add up, because volume adds across rectangles just as area does. A 250 square foot area at 3 inches needs 62.50 cubic feet, or 2.31 cubic yards, with 125 bags of 0.5 cubic feet, which is exactly two and a half times the default 100 square foot order, as it must be. A 50 square foot area at 4 inches needs 16.67 cubic feet, or 0.62 cubic yards, with 34 bags, which is the same volume as 100 square feet at 2 inches, because 50 times 4 equals 100 times 2. Whenever two different area-and-depth combinations give the same product, they give the same order, and checking that equivalence is a quick way to catch a typing slip: if doubling the area did not double the volume, something was typed wrong.
Metric inputs follow the same method through the page’s Advanced options, where square metres and centimetres live. The default metric area of 9.29 square metres is the metric twin of 100 square feet, and the default metric depth of 7.6 centimetres is the twin of 3 inches. Entering 20 square metres at the default depth gives 53.68 cubic feet, or 1.99 cubic yards, with 108 bags, and the page shows the litres figure of 1,520.00 alongside, which is the number to compare against a supplier who quotes in litres or cubic metres. The small difference between the metric coverage figure of 108.28 square feet per cubic yard and the imperial 108.00 is rounding in the unit conversion, not a different method: the volume underneath is the same, and the bag count, which is what you actually buy, follows the cubic feet.
Bags, bulk and weight: buying the volume you computed
Once the volume is known, the bag count is a division followed by rounding up, and the rounding is the whole story. The calculator divides cubic feet by the bag size and rounds up to the next whole bag, because a supplier cannot sell you a third of a bag and a shortfall of rock is worse than a small surplus. At the default, 25.00 cubic feet divided by 0.5 cubic feet per bag is exactly 50.00, so the order is 50 bags with nothing left over. At 2 inches, 16.67 cubic feet divided by 0.5 gives 33.33 exact bags, which rounds up to 34. At 4 inches, 33.33 cubic feet gives 66.67 exact bags, which rounds up to 67. The page shows the exact figure alongside the rounded order precisely so that you can see how much of the last bag is genuinely needed and how much is rounding: in the 4-inch case, two thirds of the last bag is needed, so the rounding costs little, while in a case that lands just over a whole number, nearly a full bag of the order is rounding, and a bulk delivery may be worth comparing.
| Order (100 sq ft, 3 in unless stated) | Volume | 0.5 cu ft bags | 1 cu ft bags | 2 cu ft bags |
|---|---|---|---|---|
| Default: 100 sq ft at 3 in | 25.00 cu ft | 50 | 25 | 13 |
| 100 sq ft at 2 in | 16.67 cu ft | 34 | 17 | 9 |
| 100 sq ft at 4 in | 33.33 cu ft | 67 | 34 | 17 |
| 100 sq ft at 6 in | 50.00 cu ft | 100 | 50 | 25 |
| 250 sq ft at 3 in | 62.50 cu ft | 125 | 63 | 32 |
| Custom 2 cu ft bag, default volume | 25.00 cu ft | 50 | 25 | 13 (exact 12.50) |
The table above is drawn from the calculator’s own displayed bag counts, and it shows why the bag size you pick changes the order more than people expect. Larger bags do not just halve the count, because rounding bites differently at each size: 25.00 cubic feet is 50 small bags, 25 medium bags, or 13 large bags, and 13 large bags is 26 cubic feet, a full cubic foot more than you need, while 50 small bags is exact. That is not an argument for always buying small bags, because handling fifty bags costs time and effort that a bulk delivery avoids entirely. It is an argument for comparing the true delivered volume, not just the bag count. One cubic yard equals 27 cubic feet, which equals fifty-four 0.5 cubic foot bags, twenty-seven 1 cubic foot bags, or fourteen 2 cubic foot bags after rounding up, so a bulk price per cubic yard can be compared against a bag price by multiplying the bag price by those counts, with the rounding noted.
Weight is where the calculator’s density range does its work, and it is also where a careless reading causes trouble. The default density range of 2,400 to 2,900 pounds per cubic yard is the page’s published typical range for washed river rock, and at the default volume of 0.93 cubic yards it gives 2,222 to 2,685 pounds, or 1.11 to 1.34 tons. If your supplier quotes a different density, the Advanced options let you type it in, and the weight follows immediately: with a density range of 2,000 to 2,500 pounds per cubic yard, the same default volume weighs 1,852 to 2,315 pounds, or 0.93 to 1.16 tons. Wet rock runs heavier than dry rock, and stone size changes the voids between stones, so the top of the range is the planning figure for transport and for any surface with a load limit. A vehicle or trailer rated for one ton should not be loaded with a cubic yard of wet river rock on the assumption that the low end of the range applies.
The custom bag size in Advanced options deserves a note, because it is the field most likely to be set and then forgotten. Choosing the custom size and entering 2 cubic feet at the default volume gives 13 bags with an exact figure of 12.50, which is the same as the standard 2 cubic foot bag count, as it must be, because the custom size only changes the divisor. The custom row appears only when the custom size is selected, so a custom figure typed while a standard size is selected does nothing, and a custom size left selected with an old figure in it will quietly govern the next order. Check the bag-size label in the result, which names the size it used, before you trust the count: at the default it reads “Bags (0.5 cu ft)”, and after a custom 2 cubic foot selection it reads “Bags (2.00 cu ft)”. That label is the calculator telling you which divisor it applied, and it is worth reading every time.
Stone size, fabric, and ordering without regret
Stone size is a use decision first and a looks decision second, and the page’s own guidance sorts it by where the stone will live. Small stone of 0.5 to 1 inch suits paths and beds you walk on, because it settles into a surface that is comfortable underfoot and does not roll away easily. Medium stone of 1 to 2 inches suits borders and drainage, where it stays visible, lets water through, and is heavy enough not to wash out in ordinary rain. Larger stone of 2 to 4 inches suits slopes and dry creek beds, where its weight is the point: it stays put on a slope and reads as a deliberate watercourse rather than a scattered path. Choosing by looks alone inverts this: large stone on a walking path is uncomfortable and unstable, and small stone on a slope migrates downhill with the first heavy rain. If you are torn between two sizes, buy the size that suits the job and let colour be the tiebreaker within that size, not across sizes.
Landscape fabric belongs under rock in beds and paths, and the reason is mechanical rather than cosmetic. Fabric stops weeds pushing through from below and stops the rock sinking into the soil over time, which is what turns a crisp rock bed into a muddy one with stones disappearing into it. For drainage strips, the fabric must stay permeable so water still flows, which means a woven or non-woven landscape fabric rather than an impermeable sheet: a plastic sheet under a drainage strip defeats the strip. Overlap fabric joins generously and pin the edges, because a gap in the fabric becomes a weed chimney and a sinking patch within a season. Fabric does not change the volume calculation, and it should not: the rock still needs its full depth over the fabric, and skimping on depth because fabric is present is how a bed ends up thin enough for weeds to root in the rock layer itself.
Pea gravel is the one substitution the page explicitly blesses, with a condition. The volume maths is identical, because area times depth does not care what the stone is called, so the cubic yard and bag figures carry over exactly. The weight range may differ slightly by stone type, so the density fields should be adjusted if your supplier quotes a density for the pea gravel. That condition matters more than it looks: pea gravel is typically smaller and rounder, which changes how it packs and how it moves underfoot, so a pea gravel path wants the small-stone depth and edging treatment even though its volume order is computed the same way. Do not carry over the river rock weight range to a different stone without checking, and do not carry over the river rock size guidance either: pea gravel’s walking comfort comes from its small size, and its tendency to scatter comes from the same property.
Ordering without regret comes down to four checks. One: measure the area in rectangles and add them, rather than guessing a single length and width for an irregular bed. Two: measure depth in several places and plan on the deeper readings, because volume follows average depth and dips do not cancel. Three: read the bag-size label in the result and the exact-bags figure beside it, so you know how much of the order is rounding and whether bulk delivery beats bags. Four: plan transport on the top of the weight range, and confirm the supplier’s density if it differs from the page’s 2,400 to 2,900 pounds per cubic yard. A small surplus of rock is useful: it tops up thin spots after the first settling. A shortfall stops the job half done, and a second delivery of a small quantity costs more per yard than the first. The calculator rounds bags up for exactly this reason, but rounding up by one bag does not cover a depth mismeasured by an inch across a large bed, so the measuring checks matter more than the rounding does.
Worked orders, checked against the calculator
The orders below were run through the page’s own calculator, and every figure quoted is the figure it displays. The default order is 100 square feet at 3 inches with a 0.5 cubic foot bag: 25.00 cubic feet, 0.93 cubic yards, 707.92 litres, 0.71 cubic metres, 50 bags, an exact bag figure of 50.00, a weight range of 2,222 to 2,685 pounds or 1.11 to 1.34 tons, and coverage of 108.00 square feet per cubic yard. Everything else in this section is a variation on that order with one input changed, so you can see exactly what each input does.
| Order | Volume shown | Bags (0.5 cu ft unless stated) | Weight shown |
|---|---|---|---|
| Default: 100 sq ft, 3 in, 0.5 cu ft bag | 25.00 cu ft, 0.93 cu yd | 50 (exact 50.00) | 2,222 – 2,685 lb |
| 100 sq ft, 2 in | 16.67 cu ft, 0.62 cu yd | 34 (exact 33.33) | 1,481 – 1,790 lb |
| 100 sq ft, 4 in | 33.33 cu ft, 1.23 cu yd | 67 (exact 66.67) | 2,963 – 3,580 lb |
| 100 sq ft, 6 in | 50.00 cu ft, 1.85 cu yd | 100 (exact 100.00) | 4,444 – 5,370 lb |
| 200 sq ft, 3 in | 50.00 cu ft, 1.85 cu yd | 100 (exact 100.00) | 4,444 – 5,370 lb |
| 250 sq ft, 3 in | 62.50 cu ft, 2.31 cu yd | 125 (exact 125.00) | 5,556 – 6,713 lb |
| 50 sq ft, 4 in | 16.67 cu ft, 0.62 cu yd | 34 (exact 33.33) | 1,481 – 1,790 lb |
| 20 sq m, default depth (metric) | 53.68 cu ft, 1.99 cu yd | 108 (exact 107.36) | 4,771 – 5,765 lb |
| Default volume, custom 2 cu ft bag | 25.00 cu ft, 0.93 cu yd | 13 (exact 12.50) | 2,222 – 2,685 lb |
| Default volume, density 2,000-2,500 lb/cu yd | 25.00 cu ft, 0.93 cu yd | 50 (exact 50.00) | 1,852 – 2,315 lb |
Three equivalences in that table are worth checking, because each one catches a different kind of error. First, 100 square feet at 6 inches and 200 square feet at 3 inches give the same order, because 100 times 6 equals 200 times 3: both give 50.00 cubic feet, 1.85 cubic yards, 100 bags and the same weight range. Second, 100 square feet at 2 inches and 50 square feet at 4 inches give the same order, because 100 times 2 equals 50 times 4: both give 16.67 cubic feet, 0.62 cubic yards, 34 bags and 1,481 to 1,790 pounds. Third, changing the bag size or the density never changes the volume: the custom 2 cubic foot bag row and the changed-density row both keep the default 25.00 cubic feet and 0.93 cubic yards, and only the bag count or the weight moves. If you ever see the volume move when you change only the bag size, you have changed something else by accident, and the volume row is the place to look first.
The metric row carries its own lesson. Twenty square metres at the default depth gives 53.68 cubic feet and 1.99 cubic yards with 108 bags, and the litres figure is 1,520.00, which is the figure to hand a supplier who quotes in litres. The coverage figure in that row reads 108.28 square feet per cubic yard rather than the imperial 108.00, which is conversion rounding in the metric path, not a different answer: the bag count and the volume are what you order, and both follow the cubic feet. When a supplier’s quote and the calculator disagree by a small amount, check first whether one of you is quoting litres, cubic metres, cubic feet or cubic yards, and convert before assuming either figure is wrong. Most such disagreements are unit disagreements, and the calculator shows all four volume units precisely so that the conversion is visible rather than guessed.
The depth ladder: one area, four depths, four orders
Depth is linear in volume — every extra inch on 100 sq ft is 8.33 cubic feet and 0.42 tons.
For 100 sq ft at the 100 lb-per-cubic-foot density this calculator uses, 2 inches of rock is 16.67 cubic feet (0.62 cubic yards, 0.83 tons); 3 inches is 25.00 cubic feet (0.93 yards, 1.25 tons); 4 inches is 33.33 cubic feet (1.23 yards, 1.67 tons); 6 inches is 50.00 cubic feet (1.85 yards, 2.50 tons). Each inch adds the same volume, so the ladder is a straight line — and the commonest ordering error is forgetting that depth is a multiplier, not a detail: ordering for 3 inches and spreading to 4 leaves a quarter of the bed bare, or a quarter of the order unused.
Add the 10% waste and settling allowance before ordering, not after: 1.38 tons at 3 inches, 1.83 at 4 inches, 2.75 at 6 inches for the same 100 sq ft. The allowance covers uneven ground, the rock that works down into the soil, and the edges that always take more than the plan. Bulk orders are priced per cubic yard, so the yard figure is the one to quote — compare the delivered volume, not the headline price, when choosing between bulk and bags. Depth, density and the bulk-versus-bags choice: river rock explained.
| Depth (100 sq ft) | Cubic feet | Cubic yards | Tons | Tons + 10% |
|---|---|---|---|---|
| 2 in | 16.67 | 0.62 | 0.83 | 0.92 |
| 3 in | 25.00 | 0.93 | 1.25 | 1.38 |
| 4 in | 33.33 | 1.23 | 1.67 | 1.83 |
| 6 in | 50.00 | 1.85 | 2.50 | 2.75 |
Odd shapes and slopes: measuring what is not a rectangle
Split the shape, add the rectangles, and add extra for the slope — the calculator only divides what you measure.
Most beds are not rectangles. Split an odd shape into rectangles, measure each, and add the areas — a curve becomes two or three rectangles with small errors that mostly cancel, while a single guessed rectangle carries its error whole. For a circle, use π × radius²; for a triangle, half the base times the height. The calculator shows all four volume units precisely so the conversion is visible rather than guessed, but it cannot correct an area that was never measured: the area is the input everything else trusts.
Slopes deserve their own allowance on top of the 10%. Rock migrates downhill in rain and underfoot, so a slope needs greater depth at the top and a deeper edge at the bottom to hold the line — and a drainage strip on a slope is a place where 4 inches is the working minimum, not the generous choice. Measure the slope’s area as the slope surface, not its footprint: the surface is longer than the plan, and the difference is the rock you will be short. When in doubt, order the deeper figure; rock left over landscapes the next bed, while rock short leaves this one bare.
Frequently asked questions
How much river rock do I need for 100 square feet?
At 3 inches deep, 100 square feet needs 25 cubic feet, which is 0.93 cubic yards — fifty 0.5 cubic foot bags. At 2 inches it drops to 0.62 cubic yards, and at 4 inches it rises to 1.23 cubic yards.
How many bags of river rock are in a cubic yard?
One cubic yard is 27 cubic feet, so it equals fifty-four 0.5 cubic foot bags, twenty-seven 1 cubic foot bags, or fourteen 2 cubic foot bags after rounding up. Bulk delivery is usually cheaper than bags once you pass about a yard.
How heavy is a cubic yard of river rock?
Typically 2,400 to 2,900 pounds, or about 1.2 to 1.45 tons. Wet rock can run heavier, so treat the top of the range as the planning figure for transport.
What size river rock should I choose?
Small 0.5 to 1 inch stone suits paths and beds you walk on. Medium 1 to 2 inch stone suits borders and drainage. Larger 2 to 4 inch stone suits slopes and dry creek beds, where it stays put.
Do I need landscape fabric under river rock?
For beds and paths, yes — fabric stops weeds pushing through and stops the rock sinking into the soil. For drainage strips, use a permeable fabric so water still flows through.
Can I use this calculator for pea gravel too?
The volume maths is identical — area times depth — so the cubic yard and bag figures carry over. The weight range may differ slightly by stone type, so adjust the density fields if your supplier quotes one.
How do I enter a metric area?
Open Advanced options and use the metric fields: square metres for area and centimetres for depth. The default metric area of 9.29 square metres matches 100 square feet, and 20 square metres at the default depth gives 53.68 cubic feet, or 1.99 cubic yards, with 108 bags.
Why does the calculator round bags up instead of rounding to the nearest bag?
Because a shortfall stops the job. At 2 inches over 100 square feet the exact figure is 33.33 bags, and rounding to the nearest bag would still give 33, but 33 bags is 16.50 cubic feet against 16.67 needed, so the bed would come up short. Rounding up to 34 guarantees the computed volume is covered, and the exact figure is shown beside the order so you can see how much is rounding.
How do I measure an irregularly shaped bed?
Split it into rectangles, work out each rectangle’s area as length times width, and add the areas together, then enter the total area with your planned depth. Volume adds across rectangles exactly as area does, so a bed made of a 60 square foot rectangle and a 40 square foot rectangle orders as 100 square feet.
Should I order bulk delivery or bags?
Compare the delivered volume, not just the headline price. One cubic yard is 27 cubic feet, or fifty-four 0.5 cubic foot bags after rounding up, so multiply a bag price by 54 to compare it with a per-yard bulk price. Bags suit small orders and sites a truck cannot reach; bulk usually wins on larger orders, and the calculator’s cubic yard figure is the number to compare against the bulk quote.
How much river rock do I need for 100 sq ft at 3 inches deep?
25 cubic feet, which is 0.93 cubic yards or 1.25 tons at the 100 lb-per-cubic-foot density this calculator uses. Add the 10% waste and settling allowance before ordering — 1.38 tons — to cover uneven ground, rock working into the soil, and edges. Bulk orders are priced per cubic yard, so quote the yard figure when comparing suppliers.
Should I order bulk delivery or bags?
Compare the delivered volume, not the headline price. One cubic yard is the number to compare against the bulk quote; bags are the fallback for small jobs, where the per-yard cost is higher but the quantity is exact and the handling is easier. For anything over a few cubic feet, bulk is usually cheaper per yard — and the calculator’s cubic-yard figure is the one to hand the supplier.
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Disclaimer: This calculator gives planning estimates for landscaping. Actual delivered volume depends on the supplier, stone size and compaction, and weight varies with moisture. Confirm the final quantity with your supplier before ordering.