PSU Calculator – How Many Watts Does Your PC Need?
Pick your processor and graphics card — or type in any wattage of your own — and this page adds up the whole build: board, memory, drives, fans and the little things. Then it gives you two honest numbers, the smallest standard power supply that stays safe and the size that runs cool, quiet and ready for spikes, because a PC’s parts list and a PSU’s label are only half the story each.
Your build
Advanced options — memory, storage, cooling, USB extras, overclocking and efficiency rating
Memory, storage and cooling
These advanced options are already included in the result with their default values — open Advanced options to change them.
🔒 Everything is calculated in your browser — your build never leaves your device.
Your power budget
Where the watts go
Minimum, recommended — what is the difference?
The minimum, 550 W, keeps a 20% cushion over this build’s 445 W draw, so it works — but it will run warm and closer to its limit whenever the graphics card spikes. The recommended 650 W keeps about 40% in reserve, which is where a good unit is quietest and most efficient, and it leaves the door open to a hungrier graphics card later. Sizes are the standard ladder: 450, 550, 650, 750, 850, 1000 and 1200 W.
Spikes, honestly: a modern graphics card can gulp far past its rated watts for a few thousandths of a second — reviewers have measured flagship cards spiking hundreds of watts above their board power. No average-based estimate can chase a spike, which is precisely why the recommended tier carries its 40%: it is the spike allowance, not padding.
- The two big eaters come first — processor and graphics card at the manufacturer’s own published wattages, or any custom wattage you type.
- The supporting cast counts too — board, memory, drives, fans and USB extras, the small watts most rough guesses forget.
- Buy headroom, not just watts — the minimum is the first standard size at or above draw times 1.2, the recommended at draw times 1.4, so the supply lives in its efficient, quiet middle.
Your draw against the recommended size
A power supply is happiest in the middle of its range. The bar below fills to your estimated draw inside the recommended unit’s capacity — the marked line is the smallest size that would still be safe.
Your 445 W of estimated draw fills about 68% of the recommended 650 W unit. The dashed line marks the 550 W minimum — a build should never plan to live right up against it.
Why we do not just match your parts list to a label
A parts list is an average of good behaviour. Real systems misbehave in milliseconds: graphics cards spike, processors hold turbo longer than their base rating suggests, and a cold drive spins up hungry. Two different supplies can also wear the same wattage label with very different quality underneath. That is why this calculator answers with a cushion built in — the minimum for a tight budget, the recommended for a machine that stays quiet and keeps its options open.
Pairs well with this calculation
Building or tuning the rest of the machine? These sit naturally next to a power budget.
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How to size a power supply in three steps
Start with the two big eaters
The processor and graphics card take the overwhelming share of any gaming PC’s power. Pick yours from the presets — every figure is the manufacturer’s own published wattage — or type a custom value for anything unusual.
Add the supporting cast
Motherboard, memory sticks, drives and fans are individually small — a few watts each — but a loaded case carries a dozen of them. Count them honestly; 40 to 90 W of “small stuff” is normal and it is the part most rough guesses forget.
Buy headroom, not just watts
Take the recommended size when you can. It keeps the supply in its efficient, quiet middle range, absorbs power spikes without shutdowns, and usually survives your next graphics card. The minimum is the tight-budget floor, not a target.
How the PSU calculator works
estimated draw = CPU + GPU + motherboard + memory + storage + fans + USB extras
The tiers. Power supplies come in standard sizes — 450, 550, 650, 750, 850, 1000 and 1200 W. The minimum is the first size at or above your draw × 1.2, which guarantees at least 20% headroom. The recommended is the first size at or above draw × 1.4. Component watts are rounded per part first, so the rows you see always add up exactly to the total shown. With the overclocking switch on, the processor is counted at 115% and the graphics card at 110% before rounding.
The example on this page. A Core i9-14900K (125 W) and an RTX 4070 SUPER (220 W) on a 60 W board, with 2 memory sticks (10 W), one SSD (8 W), four fans (12 W) and 10 W of USB extras: 125 + 220 + 60 + 10 + 8 + 0 + 12 + 10 = 445 W. Minimum: 445 × 1.2 = 534, so the first size that fits is 550 W. Recommended: 445 × 1.4 = 623, so 650 W — which the build then loads to 445 ÷ 650 ≈ 68%.
Two quick variations. Tick overclocking and the same build estimates 486 W (processor counted at 144 W, card at 242 W), which lifts the recommendation to 750 W. Swap the card for an RTX 4090 instead, and the total becomes 675 W — minimum 850 W, recommended 1000 W. That jump is the honest cost of a flagship card: it is never just the card’s own 450 W label, it is the headroom the card demands around it.
The wall figure. A PSU’s rating describes the power it can deliver to parts, not what it draws. At 90% efficiency, delivering 445 W means pulling 445 ÷ 0.90 ≈ 494 W from the socket; the rest leaves as heat. Efficiency changes the wall number and your electricity bill — never the size your parts need.
Going deeper
A graphics card’s rated board power is an average, and modern cards do not draw power evenly. Independent reviewers who measure with fast enough equipment — oscilloscope-grade capture, not a wall meter — have repeatedly caught high-end cards spiking to roughly double their rated power for periods measured in microseconds: an RTX 4090-class card averaging 450 W can flash past 600 W at the peak of a spike, and its predecessors were worse behaved still.
Those flashes matter because a power supply’s protection circuits watch for exactly this. If a spike crosses what the unit can deliver, its over-power protection can trip and the PC shuts off instantly — mid-game, mid-render — even though every average said the supply was big enough. It is the single most common cause of “my PC randomly dies under load” with a new graphics card.
The industry has answered in two ways. The ATX 3.0 and 3.1 standards require a compliant supply to tolerate excursions up to 200% of its rating on the graphics-card connector for 100 microseconds, so a modern, certified unit shrugs off spikes that would trip an older design of the same wattage. And builders answer with headroom — which is what the recommended tier on this page is. Buying draw × 1.4 plus an ATX 3.x unit is the belt-and-braces combination; the 20% minimum tier assumes a quality modern unit and a card with manners.
No power supply is perfect: some of what it pulls from the wall becomes heat inside the unit instead of power for your parts. The 80 Plus programme certifies how much survives. At half load, the tiers convert roughly 85% (White), 88% (Bronze), 90% (Gold), 92% (Platinum) and 94% (Titanium) — the figures the efficiency picker above uses. Two honest consequences follow.
First, the sticker size is about output, not input. A 650 W Gold unit delivers up to 650 W to the PC and will pull around 722 W from the wall doing it. Size for your parts; use efficiency only to predict heat, noise and the bill. Second, efficiency is a curve, not a constant: most units peak near half load and sag at both extremes, which is another quiet argument for the recommended size — a build drawing 445 W sits at 68% of a 650 W unit, close to the peak, but at 89% of a strained 500 W-class unit, past it.
What is it worth in money? Run the example build three hours a day: at the wall it pulls about 494 W with a Gold unit, 506 W with Bronze, 524 W with White. Gold versus White saves roughly 30 W — about 33 kWh over a year of daily sessions. Real, but modest: buy the better efficiency tier for the quieter fan and cooler case as much as for the savings.
The tier ladder: three builds, three recommendations
Power supplies come in standard sizes — 450, 550, 650, 750, 850, 1000 and 1200 W — and this page picks the first size at or above your draw times 1.2 for the minimum and times 1.4 for the recommended. Every row below is a build this page itself describes or returns.
| Build | Estimated draw | Minimum (draw × 1.2) | Recommended (draw × 1.4) | Load on recommended |
|---|---|---|---|---|
| Default: i9-14900K + RTX 4070 SUPER | 445 W | 550 W | 650 W | 68% |
| Same build, overclocking on | 486 W | 650 W | 750 W | — |
| Same build, RTX 4090 instead | 675 W | 850 W | 1000 W | 68% |
The default row is the page’s own example, worked in full: a 125 W processor and a 220 W graphics card on a 60 W board, with 2 memory sticks (10 W), one SSD (8 W), four fans (12 W) and 10 W of USB extras, totalling 125 + 220 + 60 + 10 + 8 + 0 + 12 + 10 = 445 W. The minimum is the first standard size at or above 445 × 1.2 = 534, which is 550 W; the recommended is the first size at or above 445 × 1.4 = 623, which is 650 W, and the build then loads that unit to 445 ÷ 650 ≈ 68%. The overclocking row shows what the page’s multipliers do: with the switch on, the processor counts at 115% (125 W becomes 144 W) and the card at 110% (220 W becomes 242 W), lifting the draw to 486 W and the recommendation to 750 W. The flagship row is the honest cost of a top card, verified on this page: swapping in the 450 W RTX 4090 lifts the draw to 675 W, the minimum to 850 W and the recommendation to 1000 W — never just the card’s own label, but the headroom the card demands around it.
The gap between the two tiers is the whole philosophy of the page in one number. The minimum is the tight-budget floor: it works, but it runs warm and close to its limit whenever the graphics card spikes. The recommended keeps about 40% in reserve, which is where a good unit is quietest and most efficient, and it usually survives your next graphics card. Buying the minimum when you plan to upgrade the card within the unit’s life is false economy — the upgrade will very likely demand the recommended tier anyway, and you will buy the supply twice. Buying the recommended when you will never upgrade is not waste, either: the unit runs in its efficient middle range for its whole life, its fan stays slow, and spikes have somewhere to go.
Efficiency and the wall: what the rating does not say
A power supply’s rating describes the power it can deliver to parts, not what it draws from the wall — and confusing those two is the most common misunderstanding about PSUs. At 90% efficiency, delivering the default build’s 445 W means pulling 445 ÷ 0.90 ≈ 494 W from the socket; the rest leaves as heat. The page’s own efficiency tiers, quoted at half load, are roughly 85% (White), 88% (Bronze), 90% (Gold), 92% (Platinum) and 94% (Titanium). Dividing the same 445 W draw by each tier gives the wall figure for that tier: about 524 W at White (445 ÷ 0.85), about 506 W at Bronze (445 ÷ 0.88), about 494 W at Gold, about 484 W at Platinum (445 ÷ 0.92) and about 473 W at Titanium (445 ÷ 0.94). The spread from the cheapest tier to the best is about 51 W on this build — real money over years of heavy use, but not a reason to buy a bigger unit: efficiency changes the wall number and your electricity bill, never the size your parts need. A 650 W Gold unit at full load pulls about 722 W from the wall (650 ÷ 0.90), which is the figure to check against the circuit it sits on, not the 650 W on the sticker.
There is a second efficiency lesson hiding in the load percentage. Supplies are most efficient in their middle range, which is another way of saying the recommended tier is not just about spikes — it is about where the unit spends its life. A 445 W build on a 650 W recommended unit sits at about 68% load, near the middle; the same build on a 1200 W unit would sit at 37%, below the efficient band and paying for capacity it never uses. Oversizing has no electrical penalty worth fearing — the unit only delivers what the parts ask for, which is why a bigger supply does not use more electricity by itself — but it has a price penalty and an efficiency penalty at the bottom end. The recommended tier is the sweet spot precisely because it puts the build in the middle: efficient, quiet, with room for spikes and upgrades, and no more.
Counting the small stuff honestly
The parts after the processor and graphics card total 100 W in the default build — motherboard 60 W plus 40 W of memory, storage, fans and USB extras — which is nearly a quarter of the 445 W draw. That is the part most rough guesses forget, and the page’s own guidance says 40 to 90 W of “small stuff” is normal for a loaded case even before the motherboard. Count them honestly: a dozen small parts at a few watts each are a real load, and they are also the parts whose counts change most between builds — two memory sticks or four, one drive or five, four fans or nine. The page rounds component watts per part first, so the rows always add up exactly to the total shown; that rounding is deliberate, because a total that does not equal the sum of its visible rows is a total nobody trusts. If your build has parts the presets do not list, use the custom wattage fields with the manufacturer’s published figures — the page’s steps say every preset figure is the manufacturer’s own published wattage, and the same standard should apply to anything you type yourself. Guessed watts in, guessed recommendation out.
Spikes: why averages lie about graphics cards
A graphics card’s rated board power is an average, and modern cards do not draw power evenly. The page’s deep dive reports what independent reviewers with oscilloscope-grade capture have repeatedly caught: high-end cards spiking to roughly double their rated power for microseconds — an RTX 4090-class card averaging 450 W flashing past 600 W at the peak of a spike. Those flashes matter because a supply’s protection circuits watch for exactly this: if a spike crosses what the unit can deliver, its over-power protection can trip and the PC shuts off instantly, mid-game or mid-render, even though every average said the supply was big enough. It is the single most common cause of a new graphics card randomly killing a PC under load.
The industry has answered in two ways, and the page recommends both together. The ATX 3.0 and 3.1 standards require a compliant supply to tolerate excursions up to 200% of its rating on the graphics-card connector for 100 microseconds, so a modern certified unit shrugs off spikes that would trip an older design of the same wattage. And builders answer with headroom — which is what the recommended tier is. Buying draw × 1.4 plus an ATX 3.x unit is the belt-and-braces combination; the 20% minimum tier assumes a quality modern unit and a card with manners. If your card is known for aggressive spikes, or your supply predates ATX 3.0, treat the recommended tier as the floor, not the aspiration — and treat any random shutdown under load as a spike problem to investigate before blaming drivers, thermals or luck.
Frequently asked questions
How do I work out how many watts my PC needs?
Add the power draw of every part — processor, graphics card, motherboard, memory, drives, fans and USB devices — using the manufacturers’ published figures where you can, then leave headroom on top of the total. At least 20% extra is the safe floor, and about 40% is the comfortable zone that absorbs power spikes and upgrades. That is exactly what this page does: the parts list above is the sum, and the minimum and recommended sizes are the 20% and 40% answers rounded up to standard power supply sizes.
Is a 650 W power supply enough for an RTX 4070 SUPER?
Yes, comfortably, for a typical build. The card itself is rated at 220 W total board power, and NVIDIA’s own recommendation for a system running this card is a 650 W supply. In the default build on this page — a 125 W processor, the 220 W card and the usual supporting parts, 445 W in all — a 650 W unit sits at about 68% load, right in its efficient, quiet zone, with reserve left for the card’s brief power spikes.
What happens if my power supply is too small?
The classic symptom is a shutdown or restart the moment a game or render loads the graphics card, because that is when draw peaks and spikes hit. A protection circuit inside the supply cuts output rather than feed the system badly, so the PC simply dies mid-task. A chronically undersized unit also runs hot and loud the rest of the time. Parts are rarely damaged — the protection does its job — but the fix is always the same: a bigger, better power supply.
Does a bigger power supply use more electricity?
No. A power supply only delivers what the parts ask for — a 1000 W unit feeding a 445 W build delivers 445 W, not 1000 W. What changes with size is where the build lands on the unit’s efficiency curve, and most units are at their best between about 40% and 60% load. A sensibly oversized supply can therefore waste slightly less than a strained small one, though the difference is a handful of watts, not a bill-changing amount.
What does 80 Plus Gold actually mean?
It is an efficiency certification: the supply is tested to convert at least 87%, 90% and 87% of wall power into usable power at 20%, 50% and 100% load. Crucially, the rating describes output, so a Gold 650 W unit can deliver the full 650 W to your parts. At a 445 W draw and 90% efficiency it pulls about 494 W from the wall, and the difference — roughly 49 W — leaves the unit as heat, which is why its fan exists.
How much headroom should I leave, really?
Twenty percent is the floor: below that, graphics-card power spikes and a processor holding turbo can trip a supply under load. Around 40% is the sweet spot this page recommends, because the unit runs near the middle of its efficiency curve, its fan stays slow, spikes have somewhere to go, and a future graphics-card upgrade usually fits without replacing the supply as well. Beyond about 60% headroom you are mostly buying silence and pride — harmless, but no longer necessary.
What if my part is not in the presets?
Use the custom wattage field for that part and type the manufacturer’s published figure — the same standard the presets themselves meet. Every preset figure on this page is the manufacturer’s own published wattage, so a custom entry from the same source keeps the total honest. What breaks the calculation is not a missing preset but a guessed number: a processor or card typed 50 W too low understates the recommendation by a full tier once headroom is applied, so check the spec sheet rather than estimating.
Why are component watts rounded per part?
So the rows you see always add up exactly to the total shown. Each part’s watts are rounded first, then summed, which means the visible arithmetic never disagrees with the total by a stray watt — the kind of one-watt gap that makes people distrust an otherwise correct result. The rounding is per part, not on the total, so no watt is ever silently dropped from the sum.
Does a more efficient unit mean I can buy a smaller one?
No. The size your parts need is set by what they draw, and efficiency only changes what the unit pulls from the wall to deliver it. A 445 W build needs a 650 W recommended unit whether that unit is White or Titanium; the Titanium unit simply pulls about 473 W from the wall to deliver those 445 W, against about 524 W for a White unit. Buy the size for the parts and the efficiency for the bill — the two decisions are independent, and mixing them up is how builds end up undersized.
What does the 68% load figure mean?
It is your draw divided by the recommended unit’s rating: 445 W ÷ 650 W is about 68%. It tells you where the unit spends its life — near its efficient, quiet middle range, with room for graphics-card spikes and a future upgrade. A load near 100% means the unit is working at its limit whenever the card peaks; a load under 40% usually means you paid for capacity the build will never use. The recommended tier aims for the middle, and 68% is squarely in it.
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