PSU / PC Power Calculator
Add up the power draw of your CPU, GPU, drives and peripherals to estimate total system wattage and choose a power supply with sensible headroom.
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70% utilization leaves about 30% headroom.
Load at common PSU sizes
Based on 553 W of components at 70% target load, pick a quality unit rated 850 W or higher. Add margin if you plan to overclock or expand.
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What is the PSU / PC Power Calculator?
The PSU calculator estimates the total continuous power your PC components draw and recommends a power supply wattage with headroom for transient spikes and future upgrades.
How to use it
- 1Select or enter the wattage for your CPU and GPU.
- 2Add drives, fans, memory and any extra peripherals.
- 3Choose a target utilization (70% leaves about 30% headroom).
- 4Read the estimated load and recommended PSU size.
How it works
Total load is the sum of each component estimate. The recommended PSU size divides the total by the target load percentage so the supply runs in its efficient band rather than at its limit.
Mid-range gaming build
A 125 W CPU plus a 250 W GPU, 3 drives (~15 W), fans and memory total roughly 430 W. At a 70% target load, a 650 W unit is a comfortable choice.
Limitations & notes
- Component figures are typical estimates, not measured values.
- Overclocking, transient GPU spikes and PSU efficiency all affect real draw.
- Always check your GPU vendor’s recommended PSU rating.
Frequently asked questions
How much PSU headroom do I need?
A common target is running the power supply at 50 to 70 percent of its rating under typical gaming or work load. That leaves room for short GPU power spikes, keeps fans quieter and places the unit near its best efficiency. With this calculator's high-end example, about 795 W of components at a 70% target rounds up to a 1200 W unit, while 80% target load gives 1000 W.
Does the wattage on a PSU mean what it pulls from the wall?
No. The rating is the DC power the unit can deliver to components. Wall draw is higher because of conversion losses. An 80 Plus Gold unit is about 90% efficient at half load, so 450 W of component load draws roughly 500 W from the outlet. A 750 W PSU only draws 750 W or more if the components actually demand it.
Why do modern GPUs need a bigger PSU than their rated power suggests?
Recent high-end graphics cards produce millisecond-long power excursions that can reach well above their rated board power. Older power supplies could trip their overcurrent protection and shut the PC down. ATX 3.0 and 3.1 units are designed to tolerate these spikes. If you use an older PSU with a 300 W or larger GPU, choose a lower target utilization such as 60% to give extra margin.
What numbers should I enter for CPU and GPU power?
Use the realistic maximum under load, not the base TDP. For GPUs, the vendor's total board power is a good figure. For CPUs, use the package power limit: many desktop chips have a sustained limit well above their advertised TDP, for example 142 W or 253 W. The calculator adds fixed allowances of 5 W per RAM stick, 8 W per drive and 3 W per case fan.
Is a bigger PSU less efficient at idle?
Slightly. Efficiency drops at very light loads, often below 20% of the rating, so a 1200 W unit powering a 70 W idle desktop wastes a few more watts than a 650 W unit would. The difference is small in yearly cost. Oversizing is mainly a cost and size concern; undersizing is the real risk, because it causes shutdowns under load.
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