AI & Prompt Tools · Free tool
LLM Context Window Calculator
Check if your input + output tokens fit in any major LLM (GPT-4o, Claude, Gemini, Llama, Mistral) — see headroom and percent used.
Updated April 2026
Total needed
6,000 tokens
| Model | Context | Fits? | Headroom | Fill |
|---|---|---|---|---|
| GPT-4o | 128,000 | Yes | 122,000 | 4.7% |
| Claude Opus 4 | 200,000 | Yes | 194,000 | 3.0% |
| Claude Sonnet 4 | 200,000 | Yes | 194,000 | 3.0% |
| Gemini 1.5 Pro | 2,000,000 | Yes | 1,994,000 | 0.3% |
| Llama 3.1 | 128,000 | Yes | 122,000 | 4.7% |
| Mistral Large | 128,000 | Yes | 122,000 | 4.7% |
Headroom = context window − (input + output). Leave ~10-20% buffer for safety and future edits.
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What it does
Plan whether your prompt + expected reply fits inside a model's context window. Compares GPT-4o, Claude, Gemini, Llama, and Mistral side by side.
Runs entirely in your browser — no upload, no account, no watermark. For more tools in this category see the full tools index.
How to use it
- Enter input tokens.
- Enter expected output tokens.
- Read headroom per model.
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