PC Power Supply Calculator
Enter your component wattages to find your total power draw, get a PSU recommendation with safety margin, and see which 80 PLUS tier makes sense for your build.
Last updated: May 2026
Build presets
Enter component wattages to get a PSU recommendation.
Recommended PSU = (sum of all components) x (1 + margin%)
How to choose the right PSU wattage for your PC build
A PSU is one component where undersizing causes real damage and oversizing is just mild inefficiency. The calculation is straightforward: add up the TDP values of every component, then add a safety margin. A 20% margin is the practical standard for most builds. That margin covers startup inrush current, aging capacity loss, and the gap between rated TDP and actual peak draw.
The GPU is typically the dominant draw in a gaming PC. An RTX 4070 has a TDP of 200 W but can spike to 250 W under sustained gaming load. High-end cards like the RTX 4090 have a rated TDP of 450 W. If you are running Resizable BAR with an aggressive power limit override, real board power can approach 600 W. For those cards, a 1000 W PSU is not excessive.
PSU wattage reference table
| PSU wattage | Typical build | 80 PLUS minimum |
|---|---|---|
| 350 W | Mini-ITX, no discrete GPU | Bronze |
| 500 W | Budget gaming, GTX 1660 class | Gold |
| 650 W | Mid-range, RTX 3060 / 4060 | Gold |
| 750 W | RTX 3070 / 4070, i7 / Ryzen 7 | Gold |
| 850 W | RTX 3080 / 4080, i9 / Ryzen 9 | Gold |
| 1000 W | RTX 3090 / 4090, extreme OC | Platinum |
Sizing the supply that feeds the circuit
The supply rating is not an afterthought: it is what all the other circuit decisions lean on. Total the connected load first, then add headroom before you choose a unit. The order a circuit comes together in:
- Size the conductor. Load current, run length and the allowable voltage drop give the minimum cross-section. The wire gauge calculator checks ampacity and drop together.
- Confirm the voltage drop on the run. A wire that is fine for current can still lose too much voltage over distance. The voltage drop calculator checks the run against the 3% IEC limit.
- Protect the cable with a fuse or breaker. Protection is rated to the conductor's ampacity, not the load alone. The fuse calculator sizes it correctly.
- Fit the cables in conduit. Bundled cables derate and a packed conduit fails inspection. The conduit fill calculator checks the cross-section against fill limits.
- You are here: size the supply behind the circuit. Add the wattage of every connected load, then add 20 to 30 percent headroom. The calculator above does this totalling for PC builds; the same principle applies to any supply feeding a circuit: a PSU sized right at the total load runs hot and ages fast, so I leave 20 to 30 percent headroom so it idles cool.
- Correct for power factor on reactive loads. Motors and some LED drivers draw more apparent power (VA) than real power (W). The power factor calculator converts W to the VA a generator or UPS must deliver.
- Know what it costs to run. Once the circuit feeds appliances, the appliance running cost and electricity cost calculators turn the load into a monthly figure.
Frequently Asked Questions
Why does running a PSU at exactly its rated capacity shorten its life?
PSU capacity degrades over time as capacitors age. A brand-new 500 W PSU might deliver 500 W reliably, but after 3 years of use, especially under heat, effective capacity can drop 10 to 20 percent. Component peak draw during startup and heavy load spikes also exceeds the rated TDP. A CPU running at 95 W TDP can pull 130 to 150 W during a benchmark. Running a PSU near its maximum continuously shortens its lifespan significantly and increases failure risk. A PSU operating at 50 to 80 percent of rated capacity runs cooler, quieter, and lasts longer.
What is TDP and is it the same as actual power draw?
TDP stands for Thermal Design Power. It is the amount of heat a cooling solution must be able to dissipate, not necessarily the actual power drawn from the wall. For CPUs, TDP is usually close to typical workload power draw. For GPUs, the relationship is less predictable. The RTX 4090 has a 450 W TDP, but board power measurements in GPU-intensive workloads with power limits removed can approach 600 W. AMD and Nvidia both use TDP and TGP (Total Graphics Power) figures that reflect sustained gaming loads, not peak transient spikes. When sizing a PSU for a high-end GPU, add 10-25% to the quoted TGP figure for headroom.
Does a bigger PSU waste electricity at idle?
No, a larger PSU does not draw more power just because it has higher capacity. A 1000 W PSU powering a 100 W system draws roughly 100 W plus conversion losses, not 1000 W. However, PSU efficiency is load-dependent. Most 80 PLUS units are most efficient between 50-80% load and least efficient below 20% load. A 1000 W PSU with a 200 W draw operates at 20% load, which may be 3-5 percentage points less efficient than the same system running a 400 W PSU at 50% load. The difference is small in absolute terms, but if you are optimizing for electricity cost or heat output, matching PSU wattage to roughly twice your typical load is the practical sweet spot.
Is modular vs non-modular PSU relevant to power consumption?
No. The modular vs non-modular distinction affects cable management only, not efficiency ratings. A fully modular 80 PLUS Gold PSU and a non-modular 80 PLUS Gold PSU of the same wattage deliver the same efficiency. The 80 PLUS certification is based on electrical conversion efficiency measured at the PSU output, entirely independent of whether the cables are permanently attached or removable. Choose modularity based on your case size and how much cable management flexibility you need, not for any power draw reason.
Methodology and sources
This tool estimates the wattage your PC build needs by summing the power draw of each component, then applying a safety margin and rounding up to the next standard PSU size. It also flags the efficiency tier that suits your load.
- Method: recommended PSU = (CPU + GPU + RAM + storage + motherboard + fans + other) × (1 + margin / 100), with the default margin set to 20%. The result is rounded up to the next common PSU rating (350, 400, 450, 500, 550, 650, 750, 850, 1000, 1200, 1600 W). The load percentage shown is actual component draw / recommended PSU × 100.
- Standards and sources: standard arithmetic on manufacturer TDP / TGP figures. There is no governing wiring standard for this; the efficiency tier guidance references the 80 PLUS certification program (Bronze / Gold / Platinum), which rates conversion efficiency at the PSU output, typically most efficient between 50% and 80% load.
- Assumptions and limits: component values use rated TDP, which can understate real peak draw, GPUs especially can pull 10-25% above quoted TGP under load, so a 20% margin or higher is the practical default. Capacitor aging also reduces effective capacity over a few years. Enter realistic per-component wattages; the tool does not know your exact hardware.
Reviewed and maintained by Rick Oosterling, who builds and wires 12 V, solar and EV systems hands-on. Last reviewed: June 2026. Estimates only; component power draw, board-power overrides and real-world load vary, so treat the recommendation as a planning aid and verify against the actual specifications of the parts you buy.
Next step in this workflow
Installation fully sized: explore all electrical calculators.