Metric Conversion Calculator

Metric system conversion comes in two kinds, and everything easy or hard about it follows from which kind you are doing. Inside the metric system, conversion is a decimal shift — the numbers move, the arithmetic barely exists. Between metric and imperial, conversion is a true factor problem — one honest multiplication by a defined number. This metric conversion calculator is built around that split: the decimal shifts it does instantly in your head’s place, so to speak, and the factor crossings it does exactly.

The prefix ladder. Metric has no separate units to memorize — it has base units and prefixes, and every prefix is a power of ten. Learn ten prefixes and you own every metric unit that exists, including ones you have never met: a hectoliter you have never poured is still exactly 100 liters.

The base units. The full SI has seven base units — meter, kilogram, second, ampere, kelvin, mole and candela — and this page’s nine categories lean on four of them. Length stands on the meter, mass on the kilogram, volume in daily life on the liter (exactly 1,000 cubic centimeters — a cube 10 cm on a side), temperature on the degree Celsius, with the kelvin — the same size of degree, counted from absolute zero — underneath it in science, and time on the second; speed, pressure and energy are combinations of those same base units. Since 2019 every SI unit is defined by a constant of nature rather than an object in a vault: the meter by the speed of light, the kilogram by the Planck constant. The definitions cannot drift, chip or be lost, which is one reason conversions built on them are exact rather than approximate.

Where it came from, briefly. The system was designed in 1790s France to be nobody’s local custom: the meter was set at one ten-millionth of the distance from the pole to the equator, the kilogram as the mass of a liter of water — which is why the liter and the kilogram still interlock so neatly. The 1875 Treaty of the Meter internationalized it, and the United States has been legally metric underneath ever since: the Metric Act of 1866 made metric measures lawful, and since 1893 US customary units have been defined from the metric standards — the inch is a metric unit in a costume, which is precisely why every conversion on this page can be exact.

Inside metric: move the point. Metric to metric, the prefix is the conversion. 1.5 kilometers is 1,500 meters is 150,000 centimeters — the decimal point walks three places for kilo-to-base, two more for base-to-centi, and no multiplication table is involved. The classic error is walking the point the wrong way: centimeters are smaller than meters, so the number must get bigger as you go down the ladder — 1.5 m is 150 cm, not 0.015. If the size of the number and the size of the unit disagree about direction, the point walked the wrong way.

Across the border: multiply once. Imperial units are no longer independent measures — since 1959 they are defined in metric: an inch is exactly 25.4 millimeters, a pound exactly 0.45359237 kilograms. So metric to imperial is a single exact multiplication (or its reverse division), worked by the converter above and charted in the next section. Exact, but never a decimal shift: 1 meter is 39.370079 inches, and no power of ten will ever make that a rounder number. Knowing which of the two problems you are holding — shift or factor — is the whole skill; the rest is arithmetic.

What the converter above covers. Fifty-six units in nine categories: eight of length (kilometer to millimeter, mile to inch), six of weight, three of temperature, seven of volume, six of area, five of speed, eight of pressure, six of energy and seven of time. Every one of them is either a prefix step inside metric or a defined factor across the border — there is no third kind of conversion on the page, which is why one small tool can honestly cover all fifty-six.

This is the metric conversion chart set for this page: four tables, metric down the left, imperial across the top. Read a row to convert metric to imperial; read it backwards — or use the converter above — for imperial to metric. Whether you arrived looking for a metric chart for a classroom wall or a metric unit conversion chart to settle a recipe, the object is the same, and every “conversion chart metric” search is really asking for these four tables with correct numbers in them. They use the exact defined factors, so a chart answer and a calculator answer never disagree. A dash means the value is too small to state honestly in that unit — a millimeter is six ten-millionths of a mile.

Length. The chart behind every metric to inches lookup: sewing patterns, screen sizes, lumber, height charts. Height is the everyday case: work in inches first, then convert — a person 5 feet 9 inches tall is 69 inches, and 69 × 2.54 = 175.26 centimeters, the figure a passport or a clinic abroad will want.

Mass. Grams and kilograms against the ounce-and-pound world of US recipes, parcels and body weight. The stone in the last column is exactly 14 pounds — it survives as Britain’s body-weight unit, which is why a metric chart aimed at US readers still owes it a column: 70 kilograms is 11.023113 stones, a number no pound figure will tell you.

Volume. US measures throughout — remember the imperial gallon is a different, larger unit (4.54609 liters), and this page always means the US gallon of 3.785411784 liters.

Temperature. Not a factor but a formula — °F = °C × 9 ÷ 5 + 32 — so the chart prints the anchor points life actually uses:

Reading the charts backwards. A metric-first chart converts imperial amounts too, by division instead of multiplication. Six feet into meters: find the meter row’s feet figure, 3.28084, and divide — 6 ÷ 3.28084 = 1.8288 m, the exact answer (6 × 0.3048). Ten pounds into kilograms: 10 ÷ 2.204623 = 4.535924 kg. The rule is symmetric with the forward one: metric to imperial multiplies by the chart figure, imperial to metric divides by it, and the converter above simply saves you choosing.

And area, briefly. The tool’s fifth category converts area on the same definitions: an acre is exactly 4,046.8564224 square meters, a hectare is exactly 10,000 square meters, and so a hectare is 2.471054 acres — the conversion that quietly reprices land listings. An American football field, end zones included, is 1.32 acres, or about 5,351 square meters — just over half a hectare.

The anchors, with their errors confessed. Four shortcuts circulate because they are nearly true, and “nearly” deserves a number. A liter is about a quart — it is 1.056688 US quarts, so the shortcut under-measures by 5.67%. A kilogram is about 2.2 pounds — truly 2.204623, so the shortcut runs 0.21% low, invisible in a kitchen and unacceptable in freight. A meter is about 3.3 feet — truly 3.28084, so the shortcut runs 0.58% high. A mile is about 1.6 kilometers — truly 1.609344, 0.58% low. Use the anchors to estimate and the charts (or the converter) to settle: that division of labor is what metric to standard conversion looks like when it is done honestly.

The kitchen, where volume pretends to be mass. European and modern baking recipes weigh ingredients in grams; American ones scoop them in cups — and a cup is a volume, not a weight, so the conversion runs through the ingredient. A cup of water is 236.588 grams, because a milliliter of water weighs a gram. A cup of all-purpose flour is about 120 grams (the standard reference figure used by King Arthur Baking), because flour packs air. A cup of granulated sugar is about 198 grams; a cup of butter is 227 grams — two sticks. Any chart that converts “cups to grams” with one number for all foods is quietly wrong about most of them; the honest conversion names the ingredient, as these do. Two more kitchen anchors worth the memory: a US stick of butter is 113 grams (4 ounces, exactly the quarter-pound it claims), and a large egg is about 50 grams in its shell — so a European recipe calling for 600 grams of eggs wants about a dozen. Oven temperatures cross with the formula instead: a European recipe’s 180 °C is 356 °F, from the temperature chart above.

The workshop, where millimeters already won. Cars, bicycles, appliances and most machinery sold in the US are engineered in metric: socket sets run 8 to 19 mm, bolts are named by their millimeter diameters (an M8 bolt is 8 mm across), and a “quarter-inch” drive is the surviving imperial label on a metric tool. A bicycle tire marked 700×25C wears its metric openly — the 25 is a width of 25 millimeters — and skis and snowboards are sold by the centimeter worldwide. What still speaks fractions is the older US stock — lumber, drill bits, sheet goods — and the bridge between the two is the fraction-to-millimeter table on the Conversion Calculator page. Even the lumber is bilingual under the paint: a dressed US two-by-four actually measures 1.5 × 3.5 inches, which is 38.1 × 88.9 millimeters — the size European drawings quote for it. Tire pressures straddle the border too: a European door-sticker figure of 2.5 bar is 36.259434 psi.

Medicine, where milli- and micro- do the work. The small end of the ladder is where American life is already fully metric: a standard pain-relief tablet is 500 milligrams, vitamin doses are counted in micrograms, and prescriptions are written in mg and mL everywhere. One border remains — blood glucose is reported in mg/dL in the US and mmol/L in most of the world, a factor of about 18 apart: 100 mg/dL is 5.55 mmol/L. It is the prefix ladder again, wearing a lab coat: the numbers differ, the decimal discipline does not.

Travel, where the numbers are live. Speed limits are the conversion you do at 100 km/h — which is 62.137119 mph; the common European limits of 30, 50 and 100 km/h are 18.641136, 31.06856 and 62.137119 mph, and the kilometer figure is always the bigger number, which is the trap. Airline luggage cuts the other way: the standard 23 kg checked-bag allowance is 50.70632 pounds — over the “50 lb” the same airlines print beside it, which is why a bag that passes in Frankfurt can argue in Chicago. And weather forecasts abroad become friendly once four anchors stick: 0, 10, 20 and 30 °C are 32, 50, 68 and 86 °F — freezing, cool, room, hot. Between the anchors, the converter above settles everything else.

Fuel economy, the upside-down conversion. Europe rates cars in liters per 100 kilometers — a consumption figure, where smaller is better — against America’s miles per gallon, where bigger is better. Because one side is inverted, the conversion is a division into a constant: mpg = 235.214583 ÷ (L/100 km). A car using 8.0 L/100 km returns 29.401823 mpg; a 30 mpg car uses 7.840486 L/100 km. It is the one conversion on this page where multiplying when you should divide produces not a wrong size but a wrong direction — a thriftier car looking thirstier — which makes it the fitting last example of the section’s lesson: know which problem you are holding before you reach for the factor.