How the PSU calculator works
A PSU calculator adds up the power consumption of every component in your system and turns it into a power supply wattage you can actually buy. This power supply calculator uses published figures, not guesses:
- GPU: the board power NVIDIA, AMD or Intel publish for each card. It is the biggest single load in a gaming PC.
- CPU: the maximum turbo power (Intel PL2) or package power limit (AMD PPT), not the lower TDP on the box. A Core i7-14700K can pull 253W at full load.
- Other components: about 50W for the motherboard and a few watts for each RAM stick, storage drive and case fan, plus cooling such as an AIO pump, and RGB.
- Overclocking: adds 10% to the GPU and 20% to the CPU.
The total is an estimate of your system's maximum power draw. The recommended PSU wattage adds about 30% headroom, rounds up to a standard size (550W, 650W, 750W, 850W, 1000W) and never goes below the GPU maker's own figure.
How to choose the correct PSU
- Transient spikes: modern GPUs, especially the RTX 30 series, can briefly draw well above their rated power for a few milliseconds. Headroom stops these spikes tripping the PSU's protection and causing a sudden shutdown.
- CPU pairing: a power-hungry CPU can push a configuration into the next size. The same RTX 4070 needs a 650W unit with a Ryzen 5 and 750W with a Core i9.
- Efficiency: a power supply unit is most efficient at around 40-60% load, so a little extra wattage runs cooler and quieter.
- Future upgrades: one size up now means you can fit a faster GPU later without changing the PSU.
- Form factor: standard ATX cases take any ATX unit. Small form factor builds may need SFX or SFX-L, which tops out at lower wattage.
- Quality: a well-reviewed Gold-rated unit from a known brand is safer than a bigger no-name one.
Minimum vs recommended PSU wattage
The calculator shows two numbers for your configuration:
- Bare minimum: your maximum draw plus 10%. The system should run, but with little margin for spikes, ageing components or an upgrade.
- Recommended PSU: the wattage we'd buy, with about 30% headroom.
If your current power supply wattage sits between the two, it will probably work, but a GPU upgrade is the moment to replace it.
ATX 3.1, PCIe 5.1 and the 12V-2x6 connector
RTX 40 and RTX 50 series cards use a single 16-pin power connector, now revised as 12V-2x6 with shorter sense pins so the card won't draw full power unless the plug is fully seated. ATX 3.1 units include a native 12V-2x6 cable and are designed to ride out the short power spikes of modern GPUs. You don't strictly need one: every 16-pin card comes with an adapter for three or four 8-pin PCIe cables. Either way, push the connector all the way in and don't bend it sharply near the plug.
Example PSU calculations
Mainstream gaming PC
RTX 4060 (115W) with a Ryzen 5 7600 (88W), two RAM sticks, one SSD and three fans comes to roughly 285W. With headroom that is under 450W, but NVIDIA asks for 550W for the RTX 4060, so that's our recommendation, and a 650W unit leaves room for a faster card later.
High-end gaming PC
RTX 4090 (450W) with a Core i7-14700K (253W), four RAM sticks, two SSDs, six fans, an AIO and RGB reaches about 830W, so the calculator recommends 1200W. In games the CPU rarely hits 253W at the same moment the GPU spikes, which is why NVIDIA's own power requirements for the RTX 4090 say 850W. A quality 1000W ATX 3.1 unit is the usual choice.
Buying a used GPU? Check your PSU first
A used high-end card often costs less than a new mid-range one, but it may need more power than your system has. Before you buy:
- Read the label on the side of your PSU for its wattage, efficiency rating and age. Units more than 7-8 years old, or with a lower efficiency rating than Bronze, are worth replacing before a big upgrade.
- Count your PCIe power cables. A card that needs three 8-pin plugs won't run safely from two, and splitting one cable is a bad idea on high-power cards.
- Use the table above, or check every used card against your PSU and case.