Determine CPU-GPU performance bottleneck ratio at 1080p Full HD, calculate 1-10ms microsecond transient power spikes, and determine safe ATX 3.0 power supply capacity.
NVIDIA lists 850 W as the required system power. A quality 850–1,000 W ATX 3.0 unit suits gaming. The calculator's 1,300 W is a conservative worst case that doubles GPU power for spikes.
To allow for very short load spikes above rated power. ATX 3.0 supplies are designed to ride through brief excursions, which is why vendor recommendations are lower.
Often partly. At 1080p many games are limited by the CPU, so the 4090 is used more fully at 1440p or 4K. The calculator's label is a resolution rule, not a per-game test.
The NVIDIA GeForce RTX 4090 (Ada Lovelace, launched October 2022) has 16,384 CUDA cores, 24 GB of GDDR6X memory and a rated total graphics power of 450 W, delivered through a single 16-pin 12VHPWR connector (the revised 12V-2x6 connector on newer power supplies). NVIDIA's specification page lists a required system power of 850 W.
The Intel Core i9-14900K (Raptor Lake Refresh, October 2023) has 24 cores (8 performance and 16 efficient) with 32 threads and boosts to 6.0 GHz. Intel lists a processor base power of 125 W and a maximum turbo power of 253 W. Many enthusiast motherboards ship with power limits raised above Intel's defaults, so the chip can sustain more than 253 W in all-core work unless you set the limits yourself. After instability reports on 13th- and 14th-generation desktop chips in 2024, Intel released microcode updates and a set of recommended default settings; updating the motherboard BIOS is the first step for any new build with this CPU.
The doubling of GPU power models short spikes. High-end graphics cards change load very quickly, and for a few milliseconds or less they can draw well above their rated power. Older power supplies sometimes tripped over-current protection on these spikes and shut the PC down. The ATX 3.0 power-supply standard addressed this by requiring supplies to ride through brief excursions well beyond their label, up to about twice rated power for around 100 microseconds, and by defining the 12VHPWR connector's power signalling.
| Step | Calculation | Result |
|---|---|---|
| Continuous draw | 450 + 253 + 120 | 823 W |
| Transient estimate | (450 × 2) + 253 + 120 | 1,273 W |
| Rounded PSU size | next 100 W | 1,300 W |
That is much higher than NVIDIA's 850 W recommendation, and the difference is worth understanding rather than ignoring. NVIDIA's figure assumes a typical gaming system and a quality ATX 3.0 supply that tolerates spikes by design. The calculator instead adds a full second GPU's worth of headroom and assumes the CPU sits at its 253 W limit at the same moment, which is a worst case that rarely happens in games. Sensible readings:
A few variations, computed with the same formula: lowering the CPU to its 125 W base power gives 1,145 W, or 1,200 W rounded; raising it to 320 W gives 1,400 W; swapping in a 285 W card such as the RTX 4070 Ti gives 943 W, or 1,000 W rounded.
At 1920 × 1080 the GPU renders few pixels per frame, so frame rate is often limited by how fast the CPU can prepare frames. Reviewers commonly found that an RTX 4090 at 1080p leaves headroom unused in many games even with the fastest CPUs. The calculator's bottleneck label is a simple rule based on the resolution you choose, so it will say "CPU Bound" at 1080p, "Well Balanced" at 1440p and "GPU Bound" at 4K for any pair of parts. It does not simulate particular games. If you bought a 4090, 1440p high-refresh or 4K is where it is used fully; at 1080p, a cheaper card often gives similar frame rates.