RTX 4090 vs RTX A6000
The RTX A6000 holds 43 models from our catalog that the RTX 4090 cannot fit at Q4_K_M, and decodes about 24% slower on memory bandwidth (768 GB/s against 1008 GB/s). Decode speed on a memory-bound workload scales with bandwidth, so that ratio is the number that matters once the model fits at all.
Specs side by side
| Spec | RTX 4090 | RTX A6000 |
|---|---|---|
| VRAM | 24 GB | 48 GB |
| Memory bandwidth | 1008 GB/s | 768 GB/s |
| TDP | 450 W | 300 W |
| Models that fit (Q4_K_M) | 417 of 506 | 460 of 506 |
What the extra VRAM actually buys
43 models in our catalog fit on the RTX A6000 at Q4_K_M but not on the RTX 4090. The largest of them:
Qwen 2 VL 72B InstructQwen 2.5 VL 72B InstructMolmo 72BQwen 2 72BQwen 2 72B InstructQwen 2.5 72B
Largest model each can run
At Q4_K_M the biggest fit in our catalog is Seed-OSS 36B Instruct (22.1 GB) on the RTX 4090, and Qwen 2 VL 72B Instruct (44.3 GB) on the RTX A6000. Both figures are weights plus runtime overhead; KV cache for your context is extra.
Power and running cost
At 8 hours a day the RTX 4090 draws about 108 kWh a month against 72 kWh for the RTX A6000 — a difference of 36 kWh. Multiply by your own tariff; we do not assume one. Board TDP is the rated figure, not measured draw.
FAQ
RTX 4090 vs RTX A6000: which should I buy for local AI?
The RTX A6000 fits 460 of the 506 models in our catalog at Q4_K_M against 417 for the RTX 4090, and has about 0.8× the memory bandwidth, which is what sets decode speed once a model fits. If the models you run already fit the RTX 4090, the extra spend buys context length and speed, not a new model tier.
Is the RTX A6000 faster than the RTX 4090?
No — despite the larger VRAM it has lower memory bandwidth (768 GB/s against 1008 GB/s), so on memory-bound decoding it is roughly 24% slower. It holds bigger models; it does not run them faster. This is an upper bound from bandwidth alone, not a measured benchmark.
How much more VRAM does the RTX A6000 have?
24 GB more (48 GB vs 24 GB). That difference lets it hold 43 additional models from our catalog at Q4_K_M.
Need a third card in the mix? The interactive compare tool lines up any three. To size KV cache for your context length, use the GPU Memory Calculator.
Related matchups
Other head-to-heads involving these cards:
RTX 4090 vs RTX 5090RTX 3090 vs RTX 4090RTX 4070 Ti SUPER vs RTX 4090RTX 5090 vs RTX A6000RTX A6000 vs L40S
New to sizing? What VRAM is and why bandwidth sets decode speed cover the basics, and quantization explains the formats in the table above. Common mistakes when sizing VRAM lists the traps.