TDP (Thermal Design Power)
The maximum sustained power your GPU draws under full load — critical for PSU selection.
Definition
Thermal Design Power (TDP) is the maximum amount of heat (in watts) that a GPU's cooling solution is designed to dissipate under sustained, maximum load. For AI workloads that keep the GPU at 100% utilization for hours, TDP is the realistic sustained power draw. It determines your Power Supply Unit (PSU) size requirements.
Why It Matters
Critical for rig stability. The RTX 5090 has a 575W TDP. Adding a 125W CPU, motherboard, and drives puts total system draw at ~750W. Per the 20% headroom rule, this requires a 900W+ PSU. Running a GPU beyond its TDP budget causes system instability and hardware damage.
Real-World Example
The RTX 4090 has a 450W TDP. For a full AI rig (CPU: 125W, GPU: 450W, misc: 75W), total system TDP is ~650W. With 20% headroom, you need a PSU rated at 780W minimum — so a Corsair RM850x (850W) is the right choice.
History of TDP (Thermal Design Power)
TDP as a specification was standardized by Intel in the early 2000s to help system integrators design cooling solutions. For GPUs, TDP became critical with the power-hungry NVIDIA GeForce 7800 GTX era (2005). The AI training boom post-2020 pushed consumer GPU TDPs from ~200W (GTX 1080 Ti) to 450W (RTX 4090) and 575W (RTX 5090) in five years.