Buyer comparison / 24 GB VRAM

RTX 3090 vs RTX 4090 for local LLMs: capacity is a tie.

Q: Does an RTX 4090 fit larger local LLMs than an RTX 3090?

Not when VRAM capacity is the limiting factor. NVIDIA specifies 24GB of GDDR6X memory for both cards, so this page gives each the same 21.6 GiB planning budget after reserving ten percent. Runtime speed and efficiency are separate questions.

Q: Can an RTX 3090 or RTX 4090 run Qwen3 30B-A3B?

The fully GPU-resident INT4 32K scenario on this page reaches 20.64 GiB and fits within the 21.6 GiB planning budget on either 24GB card, but with narrow margin that still needs runtime validation.

Q: Can an RTX 3090 or RTX 4090 run Qwen3 32B at 32K?

Not under this page's fully GPU-resident INT4 planning profile. The 32K scenario reaches 27.93 GiB after cache and headroom, above the 21.6 GiB default budget for either card.

Q: Which is better for local LLMs, RTX 3090 or RTX 4090?

They tie on one-card model capacity because both have 24GB. Choose only after measuring the exact runtime, model, context, batch size, power limit, system compatibility, condition, and total cost relevant to your workload.

Both cards carry 24GB of GDDR6X. That means the same fully GPU-resident model-fit ceiling under identical assumptions. Pay for measured throughput or system value—not an imaginary VRAM advantage.

Test your exact model →

Fast verdict

Same model ceiling. Different performance class.

RTX 3090
24 GB GDDR6X · Ampere

RTX 4090
24 GB GDDR6X · Ada Lovelace

Capacity budget
24 × 0.90 = 21.6 GiB each

Decision rule
Fit first · benchmark second

Shared model boundary

These model-fit answers do not change between the cards.

Each card opens an editable, fully GPU-resident estimate. Change context, cache precision, runtime headroom, or GPU count before treating a paper fit as a deployment plan.

Qwen3 14B · INT4 · 32K14.27 GiBFits either card's planning budget → Qwen3 30B-A3B · INT4 · 32K20.64 GiBNarrow fit on either 24GB card → Qwen3 32B · INT4 · 32K27.93 GiBMisses either one-card budget → gpt-oss-20b · MXFP4 · 4K14.29 GiBFits either card's planning budget → gpt-oss-20b · MXFP4 · 128K22.56 GiBNarrow miss on either card → 70B · raw INT4 weights32.60 GiBMore than either card before cache →

Buying decision

Separate fit from delivered performance.

The RTX 4090 has a newer architecture and more CUDA cores, but those specifications do not establish tokens per second for your model and runtime. Benchmark the exact workload.

Question	RTX 3090	RTX 4090
Official memory	24 GB GDDR6X	24 GB GDDR6X
Default usable budget	21.6 GiB	21.6 GiB
One-card model ceiling	Same at equal assumptions	Same at equal assumptions
What still needs testing	Runtime, model, context, batch, power, thermals, system fit, condition, and total cost

Do not buy from one number

Capacity ties.
Both cards get the same 24GB model-fit answer under equal assumptions.

Speed needs evidence.
The exact engine, kernels, quantization, context, and batch decide delivered throughput.

Total value is local.
Include card condition, power, cooling, chassis, warranty, and your actual workload.

Primary sources

Verify the capacity claim at the source.

NVIDIA's RTX 3090 guide and Ampere architecture paper specify 24GB of GDDR6X. NVIDIA also specifies 24GB of GDDR6X for the RTX 4090. ResearchAudio's calculator applies the same reserve and model assumptions to both.

Official NVIDIA RTX 3090 user guide → Official NVIDIA RTX 4090 specifications → Open the detailed 24GB model guide →

Does an RTX 4090 fit larger local LLMs than an RTX 3090?

No when VRAM is the binding constraint. Both have 24GB, so the fully resident model-fit boundary is the same under equal assumptions.

Can an RTX 3090 or RTX 4090 run Qwen3 30B-A3B?

The 32K INT4 scenario reaches 20.64 GiB and fits the 21.6 GiB planning budget narrowly on either card. Validate the exact runtime before deployment.

Can an RTX 3090 or RTX 4090 run Qwen3 32B at 32K?

Not under this fully GPU-resident profile. Cache and headroom lift the estimate to 27.93 GiB, above either card's default budget.

Which is better for local LLMs, RTX 3090 or RTX 4090?

Capacity alone cannot choose between them. Measure throughput and total system value for your engine, model, context, batch, power, and hardware constraints.