Quick answer: The RTX 4090 is roughly 60-70% faster for LLM inference than the RTX 3090, but the 3090 at ~$820 used offers unbeatable VRAM-per-dollar. If budget is tight, the 3090 still runs every model the 4090 can.
Check NVIDIA GeForce RTX 4090 on Amazon→Buy on Shopee SG→Why this comparison matters
Both the RTX 4090 and RTX 3090 pack 24GB of VRAM — the magic number that lets you run 13B models at high quantization and 34B models at Q4. But they sit at wildly different price points in 2026. The 4090 retails around $2,200 new while 3090s go for roughly $820 on the used market. That raises a real question: is the newer card worth nearly three times the money?
Spec comparison
| Spec | RTX 4090 | RTX 3090 |
|---|---|---|
| VRAM | 24GB GDDR6X | 24GB GDDR6X |
| Memory bandwidth | 1,008 GB/s | 936 GB/s |
| CUDA cores | 16,384 | 10,496 |
| Architecture | Ada Lovelace | Ampere |
| TDP | 450W | 350W |
| FP16 TFLOPS | 82.6 | 35.6 |
| New price (2026) | ~$2,200 | Discontinued |
| Used price (2026) | not quoted | ~$820 |
VRAM capacity memory bandwidth Specs are manufacturer figures. Bar lengths are scaled independently per metric.
LLM inference benchmarks
Memory bandwidth drives token generation speed. The 4090 has a modest 8% bandwidth advantage, but its newer architecture and larger cache deliver bigger real-world gains.
| Model (Quantization) | RTX 4090 tok/s | RTX 3090 tok/s | Difference |
|---|---|---|---|
| Llama 3 8B (Q4_K_M) | ~95 | ~65 | +46% |
| Llama 2 13B (Q4_K_M) | ~55 | ~40 | +38% |
| CodeLlama 34B (Q4_K_M) | ~22 | ~14 | +57% |
| Yi-34B (Q4_K_M) | ~20 | ~13 | +54% |
| Mistral 7B (FP16) | ~80 | ~50 | +60% |
The 4090 wins every benchmark, but the 3090 stays well above the 10 tok/s usability threshold even on 34B models. For Ollama-specific benchmarks comparing both cards side by side, see RTX 4090 vs 3090 for Ollama.
When to buy the RTX 4090
Pick the 4090 if you:
- Run 34B models regularly and want snappy interactive speeds
- Use batch inference or serve models to multiple users
- Want the FP16 compute headroom for fine-tuning experiments
- Plan to keep the card for 3+ years
- Need lower power draw per token (the 4090 is more efficient despite higher TDP)
The 4090 is also the better long-term investment. As models grow more complex, the architecture advantages compound.
When to buy the RTX 3090
Pick the 3090 if you:
- Primarily run 7B-13B models where both cards feel instant
- Want 24GB VRAM at the lowest possible cost
- Are building a multi-GPU setup and need two 24GB cards on a budget
- Already have a system with a compatible PSU (350W is easier to handle)
- Are comfortable buying used hardware
At around $820, the 3090 gives you the same model compatibility as the 4090. You lose speed, not capability. If you are leaning toward the 3090, our used RTX 3090 buying guide for LLM walks through the inspection checklist and the specific failure modes that affect this card on the secondary market.
Value analysis
| Metric | RTX 4090 | RTX 3090 (used) |
|---|---|---|
| Cost | ~$2,200 | ~$820 |
| VRAM per $1,000 | 11 GB | 29 GB |
| 13B tok/s per $1,000 | 25 | 49 |
| Warranty | Yes | No |
The 3090 delivers nearly double the VRAM per dollar. For raw value, it wins. For performance and peace of mind, the 4090 takes it.
Common mistakes when choosing between RTX 4090 and 3090
Overpaying for speed you won’t notice — If you mostly run 7B-13B models, both cards generate tokens well above the usability threshold. The 4090’s speed advantage is most felt on 34B models. Do not pay $1,380 extra for imperceptible gains on small models.
Buying a used 3090 without testing — Mining-worn 3090s are common on the used market. Always stress test with nvidia-smi and a long inference run before finalizing a used purchase. Check for thermal throttling and VRAM errors.
Forgetting power supply requirements — The RTX 3090 draws 350W and the 4090 draws 450W. Budget for a quality 850W+ PSU with the right connectors. An underpowered PSU causes crashes under load.
Assuming the RTX 5090 is a small step up in price — it used to be. It is not now: a new 4090 is about $2,200 and the RTX 5090 is about $4,900, so the 32GB and the extra bandwidth cost roughly $2,700 more, not a few hundred. At that gap the 5090 has to be justified on its own terms rather than as a cheap upgrade, and for most people reading a 4090-vs-3090 comparison it will not be.
Our verdict
For most local LLM users running 13B models or smaller, the RTX 3090 at around $820 used is the smarter buy. You get identical model compatibility and good enough speed. The difference is now about $1,380 — enough for a second 3090 and 48GB of total VRAM, which is a better use of the money than either single card for anyone running large models. See the RTX 5090 comparison if you want the top of the range instead.
If you run 34B models daily or want the fastest single-GPU experience without going to RTX 5090 pricing, the 4090 justifies its premium.
Check NVIDIA GeForce RTX 4090 on Amazon→Buy on Shopee SG→ Check NVIDIA GeForce RTX 3090 on Amazon→Buy on Shopee SG→