A PSU calculator built on spec-sheet wattages
Choosing a power supply comes down to one question: how many watts can your PC draw at its busiest? This PSU calculator adds up your processor and graphics card from their manufacturers’ published power figures, plus the board, memory, drives, fans and USB devices, and turns the total into a recommended power supply size with the headroom rule shown in plain sight.
It also shows the graphics card maker’s own PSU figure, checks a power supply you already own, and estimates the draw at the wall and the monthly running cost in rupees, dollars, pounds or euros. Every number is editable, and the tables list their source and the date they were checked, because new parts launch all the time.
How to use the PSU calculator
- Pick your CPU. The maximum package power fills in — Intel’s Maximum Turbo Power or AMD’s PPT. Switch to base power if you limit the CPU.
- Pick your graphics card; its board power fills in. Not listed? Choose “Other” and type the figure from its spec sheet.
- Open Other parts to set how many drives, fans, RGB strips and USB devices you have.
- Keep the 80 % target load, or change it; add an overclock allowance if you overclock.
- Read the recommended wattage. Enter the PSU you own to check it, and set hours and electricity price for the running cost.
PSU Wattage Calculator features
Manufacturer figures
CPU and GPU wattages from Intel, AMD and NVIDIA specification pages, each with source and date.
Visible rule
Recommended = peak load ÷ target load, rounded up to the next common size — shown with your numbers.
GPU maker check
The card maker’s recommended or minimum PSU is shown, and the higher of the two figures is recommended.
Editable everything
Override any wattage, count or the target load; unknown parts are labelled as estimates.
Wall draw and cost
80 PLUS efficiency turns DC load into watts at the socket and a monthly cost in ₹, $, £ or €.
How the wattage is calculated
Peak load = CPU maximum package power + graphics card board power × number of cards + the other parts. With the default build — a Ryzen 7 7800X3D (PPT 162 W), an RTX 5070 (250 W), a 50 W board estimate, two memory sticks, one NVMe drive, three fans and two USB devices — that is 494 W. Divided by an 80 % target load it needs 617.5 W, so the next common size, 650 W, is recommended. NVIDIA lists 650 W for that card too.
Why 80 %? Running a power supply well below its rating leaves room for brief power spikes, keeps it in an efficient part of its range, keeps the fan quieter and allows for capacitor ageing. It is a common rule of thumb, not a standard, so the target is editable. Lower it (70 %) for more margin or an older unit.
Power spikes, ATX 3.x and the GPU maker’s figure
Modern graphics cards can draw well above their rated board power for fractions of a millisecond. Intel’s ATX 3.0 and 3.1 power supply design guides require units to ride through short excursions up to twice their rating for 100 microseconds, which is why an ATX 3.x unit with a native 12V-2×6 connector handles high-end cards more gracefully than many older designs. The card makers’ PSU figures (for example 1,000 W for an RTX 5090, 800 W for an RX 7900 XTX) assume a high-end CPU and some margin; when it is higher than the calculated size, this calculator recommends it.
Check that the supply also has the right connectors: one 12V-2×6 (12VHPWR) or enough 8-pin PCIe cables for your card, and the CPU’s 8-pin EPS leads.
Efficiency, wall draw and running cost
A PSU’s rating is what it can deliver to the parts, not what it takes from the wall. 80 PLUS levels set minimum efficiencies at 20, 50 and 100 % load: on 115 V, Bronze 82/85/82 %, Gold 87/90/87 % and Platinum 90/92/89 %; units on 230 V mains, as in India and the UK, run slightly more efficiently. The calculator interpolates the level’s efficiency at your load, gives the wall draw, and multiplies by your hours and tariff for a monthly upper-bound cost — real gaming draw is usually lower than the peak. For appliance bills see the electricity bill calculator, and for volts and amps the watt calculator.
PSU Wattage Calculator FAQ
How many watts PSU do I need?
Add your CPU’s maximum power, your graphics card’s board power and the rest of the parts (the default list here comes to about 80 W), then divide by 0.8 and round up to a common size. The PSU calculator does the sum with your exact parts.
Is a 650 W PSU enough for an RTX 5070?
With a mainstream CPU, usually yes: NVIDIA lists 650 W, and a Ryzen 7 7800X3D build estimates 494 W at peak. A 250 W-plus CPU pushes it towards 750 W.
Does a bigger PSU use more electricity?
No. A PC draws what its parts need; a larger unit does not add load. Very oversized units can be slightly less efficient at low load.
Why use the maximum turbo power and not the TDP?
Under heavy load Intel CPUs run up to Maximum Turbo Power and AMD CPUs up to PPT, both well above the base figure. Sizing for the maximum avoids shutdowns.
What about PSU calculators in India — does 230 V change the answer?
The wattage you need is the same. On 230 V the supply is a little more efficient, so the wall draw and bill are slightly lower. Enter your tariff in ₹ per unit (kWh) for the running cost.
Are the wattage tables up to date?
They were checked against manufacturer pages on 19 October 2026. New parts and factory-overclocked models differ, so check your model and type its figure if needed.