RTX 3090 24GB vs RTX 4090 24GB for local LLMs
Memory fit, speed and context compared with the same math as the advisor. Both offer about the same usable memory (23.0 GB), so the difference is mostly bandwidth (936 vs 1008 GB/s).
Verdict from the numbers
- Fit. RTX 3090 24GB fits 11 of 13 models fully at 16k context (largest: Qwen3.6 35B-A3B UD-Q4_K_M); RTX 4090 24GB fits 11 (largest: Qwen3.6 35B-A3B UD-Q4_K_M). Both fit the same set of models.
- Speed. On the 11 models that fit fully on both, RTX 4090 24GB is faster by a typical 1.2x. RTX 3090 24GB is ahead on 0, RTX 4090 24GB on 11. 7 of those comparisons use measured speeds on both sides; the rest involve at least one estimate (see the badges).
- Trade-off. Both offer about the same usable memory (23.0 GB), so the difference is mostly bandwidth (936 vs 1008 GB/s).
Where to check prices
Price tier note
We do not list prices because they move daily and differ between new and used stock. What the data does show is what the memory difference buys: both have the same usable memory, so model fit is identical and the choice comes down to speed (936 vs 1008 GB/s bandwidth). Use the Amazon links above to compare current listings and decide whether the difference is worth it for the models you want to run.
Model by model · 16k context, f16 KV cache
| Model | RTX 3090 24GB fit | tok/s | RTX 4090 24GB fit | tok/s | Faster / fits |
|---|---|---|---|---|---|
| Gemma 4 26B-A4B UD-Q5_K_M | fits fully | 112 scaled from measured | fits fully | 135 scaled from measured | RTX 4090 24GB |
| Gemma 4 31B Q4_K_M | fits fully | 39 measured | fits fully | 44 measured | RTX 4090 24GB |
| Gemma 4 12B Q8_0 | fits fully | 57 measured | fits fully | 64 measured | RTX 4090 24GB |
| Qwen3.6 27B Q5_K_M | fits fully | 36 scaled from measured | fits fully | 42 scaled from measured | RTX 4090 24GB |
| Qwen3.6 35B-A3B UD-Q4_K_M | fits fully | 159 measured | fits fully | 190 measured | RTX 4090 24GB |
| Qwen3.5 9B Q8_0 | fits fully | 86 measured | fits fully | 95 measured | RTX 4090 24GB |
| Qwen3.5 4B Q8_0 | fits fully | 138 measured | fits fully | 158 measured | RTX 4090 24GB |
| gpt-oss 20B Q8_0 | fits fully | 204 measured | fits fully | 258 measured | RTX 4090 24GB |
| gpt-oss 120B | does not fit | - | does not fit | - | - |
| Qwen3-Coder 30B-A3B Q4_K_M | fits fully | 206 measured | fits fully | 266 measured | RTX 4090 24GB |
| Mistral Small 3.2 24B Q6_K | fits fully | 37 scaled from measured | fits fully | 42 scaled from measured | RTX 4090 24GB |
| Qwen3-VL 8B Q8_0 | fits fully | 91 scaled from measured | fits fully | 102 scaled from measured | RTX 4090 24GB |
| GLM-4.5-Air | does not fit | - | does not fit | - | - |
Badges: measured medians of real llama.cpp runs; scaled from measured and estimated come from our bandwidth model. See sources and methods.
How much context fits?
Largest context where weights plus KV cache stay inside usable memory, per model that fits fully on at least one side. q8_0 KV roughly halves the cache.
| Model | RTX 3090 24GB f16 | RTX 4090 24GB f16 | RTX 3090 24GB q8_0 | RTX 4090 24GB q8_0 |
|---|---|---|---|---|
| Qwen3.6 35B-A3B | 32k | 32k | 64k | 64k |
| Gemma 4 31B | 32k | 32k | 64k | 64k |
| Qwen3-Coder 30B-A3B | 32k | 32k | 64k | 64k |
| Qwen3.6 27B | 32k | 32k | 64k | 64k |
| Gemma 4 26B-A4B | 64k | 64k | 128k | 128k |
| Mistral Small 3.2 24B | 16k | 16k | 32k | 32k |
| gpt-oss 20B | 128k | 128k | 128k | 128k |
| Gemma 4 12B | 256k | 256k | 256k | 256k |
| Qwen3.5 9B | 256k | 256k | 512k | 512k |
| Qwen3-VL 8B | 64k | 64k | 128k | 128k |
| Qwen3.5 4B | 512k | 512k | 1M | 1M |
Spec summary
| RTX 3090 24GB | RTX 4090 24GB | |
|---|---|---|
| Usable memory for model + KV cache | 23.0 GB | 23.0 GB |
| Memory bandwidth | 936 GB/s | 1008 GB/s |
| Models that fit fully at 16k | 11 of 13 | 11 of 13 |
| Models that need offload or do not fit | 2 | 2 |
| Measured data points on file | 20 | 24 |
FAQ
Which is faster for local LLMs, RTX 3090 24GB or RTX 4090 24GB?
On the 11 models that fit fully on both, RTX 4090 24GB is typically 1.2x faster (geometric mean). RTX 3090 24GB wins 0 and RTX 4090 24GB wins 11. 7 comparisons are measured on both.
Which fits more models, RTX 3090 24GB or RTX 4090 24GB?
RTX 3090 24GB fits 11 of 13 models fully at 16k context and RTX 4090 24GB fits 11.
Can I run long context on RTX 3090 24GB or RTX 4090 24GB?
At f16 KV cache, the largest-model context limits are in the table above (for example Qwen3.6 35B-A3B on RTX 3090 24GB: 32k; Qwen3.6 35B-A3B on RTX 4090 24GB: 32k). A q8_0 KV cache extends it further.
Do you state prices for RTX 3090 24GB or RTX 4090 24GB?
No. Prices change daily, so we link to Amazon search results instead and focus on measured and estimated speed and memory fit.
Related
RTX 3090 24GB · RTX 4090 24GB · Measured model pages: gpt-oss 20B · Qwen3.6 35B-A3B · Qwen3-Coder 30B-A3B · Gemma 4 31B · Qwen3.6 27B · Gemma 4 26B-A4B
More comparisons: RTX 3090 24GB vs RTX 5090 32GB · RTX 3090 24GB vs AMD RX 7900 XTX 24GB · RTX 4090 24GB vs RTX 5090 32GB · RTX 4090 24GB vs AMD RX 7900 XTX 24GB · RTX 5080 16GB vs RTX 4090 24GB · MacBook Pro 14/16 (2024) M4 Max 128GB vs RTX 4090 24GB · all comparisons
By memory: 8 GB · 12 GB · 16 GB · 24 GB · 32 GB · 48 GB · 64 GB · 96 GB · 128 GB · 192 GB · 256 GB · 512 GB