PSU Wattage Calculator
Estimate the peak power load of a desktop PC from its CPU, GPU and peripherals, and get a recommended PSU size snapped to standard ratings — with efficiency and 12 V rail notes. Runs entirely in your browser.
This calculator runs entirely in your browser. No data is sent anywhere, no account needed.
Your recommendation
- Estimated peak load
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- Load with headroom
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- Expected load on PSU
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Per-component breakdown
Transient power spikes can exceed published TDP/peak values — this calculator provides an estimate, not a measurement; real systems may need more headroom.
PSUs peak efficiency at roughly 40–60% load; an oversized PSU is not more efficient — right-size it with quality.
Build your system
How to use the PSU wattage calculator
Step by step
- Search for your CPU in the CPU picker and select it.
- Search for your GPU and select it — or skip it for APU-only / no-GPU builds.
- Set the counts of your RAM sticks, drives, fans and other peripherals.
- Pick a power mode: stock, overclocked, or power-limited / undervolted.
- Read the recommended PSU size plus the efficiency, 12 V rail and spike notes.
About the numbers
- CPU figures use published peak package power; GPU figures use published TBP (max board power).
- The load is multiplied by a fixed 1.4× headroom, then snapped up to the nearest standard rating: 450 / 550 / 650 / 750 / 850 / 1000 / 1200 W.
- Overclocking adds +20% on CPU and GPU peaks; power-limited / undervolt removes 20%.
- The 12 V rail check assumes roughly 60% of the rated watts are available on the 12 V rail — a conservative share, so a warning means the 12 V-heavy part of the build (CPU, GPU, motherboard, fans) is very close to it. Modern PSUs put most of their output on a single 12 V rail, so this is a precaution, not a verdict.
- This is an estimate from published figures, not a measurement — transient spikes can exceed them.
Use cases
Common situations where this calculator helps you pick the right PSU size.
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New high-end gaming PC
Pairing an RTX 5090-class GPU with a flagship CPU lands near the 1200 W ceiling — confirm your PSU actually covers the combined peak load before buying.
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Mid-range upgrade
Dropping an RTX 5070 into a Ryzen 5 machine typically recommends 650 W — enough headroom without paying for a unit you'll never use at full capacity.
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APU-only build
A Ryzen APU with integrated graphics, no discrete GPU: the estimate stays in the 450–550 W range, so you don't over-buy a 750 W+ unit.
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Upgrade feasibility check
Curious whether your existing 650 W PSU can handle a new GPU? Compare the recommended size against what's already in the case.
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Overclocking headroom
Planning an overclock or raising your power limits? Switch to the overclocked mode to see how much extra headroom you'll want.
Frequently asked questions
- How does this PSU wattage calculator work?
- It adds up the published peak draws of your selected CPU, GPU and peripherals (RAM, drives, fans, etc.), multiplies the total by a fixed 1.4× headroom factor, and snaps the result up to the nearest standard rating: 450 / 550 / 650 / 750 / 850 / 1000 / 1200 W. It also reports where that recommendation sits on the efficiency curve and whether the 12 V rail is near capacity. Note: it's an estimate from published figures, not a measurement.
- What PSU do I need for an RTX 5090?
- With a flagship CPU (e.g. Ryzen 9 9950X3D) and typical mid-high-end peripherals, the calculator recommends a 1200 W PSU — the maximum standard size — because the combined peak load of ~820 W exceeds what a 1000 W unit comfortably covers after headroom. For slightly less heavy CPUs you may still land at 1200 W; the 5090's 575 W board power dominates the estimate.
- What PSU size for RTX 5080, 5070, 4090 or 4070?
- Roughly: RTX 5080 with a high-end CPU → 1000 W (1200 W if overclocked); RTX 5070 with a Ryzen 5 → 650 W; RTX 4090 with a high-end CPU → 1000–1200 W; RTX 4070 with a mid-range CPU → 550 W. These match the calculator's 1.4× headroom formula; your own peripheral counts may shift the recommendation by one size.
- Is a bigger PSU better?
- Not necessarily. PSUs are most efficient at roughly 40–60% of their rated load. An oversized unit runs at low load, wastes energy, and costs more for headroom you may never use. A right-sized, high-quality unit beats an oversized cheap one.
- Are the numbers exact — what about transient power spikes?
- No — the figures are published TDP/TBP (typical/maximum sustained) draws, not measurements. Modern flagships (NVIDIA 30/40/50-series and AMD RDNA2/RDNA3) can spike well above their board power for milliseconds. This calculator flags such cards with a 'transient spikes' tag and adds a caveat: it's an estimate, and real systems may need more headroom. If you see random crashes under full load, step up one PSU size.