Computed

Qwen2.5 1.5B Instruct on an L40S

Yes — the unquantized weights fit with room for 32k tokens of context.

Change the numbers →Qwen2.5 1.5B Instruct on every card L40S across every model

Verdict

Fits at FP16

44.2 GiB usable of 48 GB

Weights (Q4_K_M)

940 MiB

2.9 GiB at FP16 · 1.5B params · 6 of 6 quant rows are measured files

KV cache

28.0 KiB per token at FP16

28 layers × 2 KV heads × 128 dimensions

Speed ceiling

260 tok/s

864 GB/s ÷ bytes read per token

Every quant, against this card

Weight bytes are the size of the real published file wherever one exists — 6 of these6 rows are measured from bartowski/Qwen2.5-1.5B-Instruct-GGUF, the rest computed from the parameter count. Max context is what the KV cache can grow to in whatever memory the weights leave behind, capped at the 32k tokens this model was trained to address.

Bars are the weight bytes at each precision; the dashed line is the usable memory of an L40S. Drawn from the computed byte counts, not sketched.

Precision	Bits/weight	Weights	Source	Fits	Max context	Ceiling
FP16 / BF16	16.00	2.9 GiB	measured file	yes	32,768 (model cap)	260 tok/s
Q8_0	8.53	1.5 GiB	measured file	yes	32,768 (model cap)	459 tok/s
Q6_K	6.60	1.2 GiB	measured file	yes	32,768 (model cap)	573 tok/s
Q5_K_M	5.83	1.0 GiB	measured file	yes	32,768 (model cap)	635 tok/s
Q4_K_M	5.11	940 MiB	measured file	yes	32,768 (model cap)	708 tok/s
Q3_K_M	4.27	786 MiB	measured file	yes	32,768 (model cap)	816 tok/s

What the context actually costs

The KV cache is 2 · layers · kv_heads · head_dim bytes per token per element — 2 · 28 · 2 · 128 · 2 B = 28.0 KiB. It depends on the key/value head count, not the attention-head count and not the parameter count. This model shares 2 KV heads across 12 query heads, which divides the cache by 6 against multi-head attention.

Context	KV cache (FP16)	KV cache (8-bit)	Plus Q4_K_M weights
4,096	112 MiB	56 MiB	1.0 GiB
8,192	224 MiB	112 MiB	1.1 GiB
32,768	896 MiB	448 MiB	1.8 GiB

The speed ceiling, and where it comes from

Generating one token reads every active weight from memory once. At FP16 / BF16 that is 2.9 GiB, plus a pass over the KV cache. An L40S moves 864 GB/s (384-bit × 18 Gbps), so the arithmetic ceiling is 260 tok/s. Treat it as a bound, not an estimate: attention overhead, kernel launches and imperfect memory access keep real runtimes at roughly 60–80% of it, and nothing pushes past it.

Where these numbers come from

The model

Parameters: 1,543,714,304
Layers: 28
Attention / KV heads: 12 / 2
Head dimension: 128
Trained context: 32,768
Checkpoint as published: 2.9 GiB

Read from Qwen/Qwen2.5-1.5B-Instruct. The parameter count is the Hub's own total over the tensor shapes, not a figure taken from the model's name.

The accelerator

Memory: 48 GB GDDR6 ECC
Bandwidth: 864 GB/s
Bus: 384-bit × 18 Gbps
Assumed usable: 92% → 44.2 GiB

Capacity and bandwidth from the vendor's specification. The bandwidth figure is checked against the bus width and data rate it derives from. The usable fraction is an assumption, not a spec: a driver context, compute workspace and any attached display come out of the same pool before a weight is loaded.

Questions this pairing answers

How much VRAM does Qwen2.5 1.5B Instruct need?

2.9 GiB for the weights at FP16 — 1.5B parameters at two bytes each — and 940 MiB at Q4_K_M. The KV cache is on top of that and is not a fixed number: this model spends 28.0 KiB per token of context, so 8,192 tokens costs a further 224 MiB. An L40S makes 44.2 GiB of its 48 GB available on the assumption below.

Can an L40S run Qwen2.5 1.5B Instruct?

Yes — the unquantized weights fit with room for 32k tokens of context. That is the weights and the KV cache together, against 44.2 GiB of usable memory.

How fast will Qwen2.5 1.5B Instruct run on an L40S?

No faster than 260 tokens/second at FP16 / BF16, and in practice below it. Decoding is memory-bound: every token reads all 2.9 GiB of weights plus the cache, and this card moves 864 GB/s. That division is the ceiling — no kernel, runtime or driver beats it, and a real runtime typically reaches 60–80% of it.

Why does the context length change how much memory Qwen2.5 1.5B Instruct needs?

Because the KV cache holds one key and one value vector per token, per layer, for the whole conversation, and it is allocated separately from the weights. This model has 28 layers and 2 key/value heads of 128 dimensions, shared across 12 query heads — grouped-query attention, which divides the cache by 6. That works out at 28.0 KiB per token. Parameter count tells you nothing about this number.

The same model on a different card

A different model on the same card

All 62 models on L40S →

Method and limits. Weight bytes are the byte size of the real published file wherever one exists, and the model's exact parameter count times the published llama.cpp bits-per-weight where it does not. That distinction is on every row above and it matters at both ends: a sub-1B model's Q4_K_M file runs a third larger than the nominal figure because k-quants keep its embedding tables at higher precision, and an already-4-bit release cannot be quantized upward at all. The KV cache is 2 · layers · kv_heads · head_dim · bytes per token, summed over layers with each sliding-window layer capped at its window. The speed figure is a roofline bound, not a benchmark: bandwidth divided by bytes read per token, which no runtime exceeds and every runtime falls short of. The usable fraction of card memory is an assumption: 92% here, which is what this lane assumes for a dedicated card — the other class assumes 75%, so it is not one number applied to every device. That is the only assumed input on this page; every other figure is computed from the model config and the card's published specification. Nothing on this page is written by a language model. Architecture from the model's published config, fetched 2026-08-07.