AI Context Window Calculator
See how much of a model context window your prompt uses and what fits
Used to estimate how many items of this size fit.
Token counts are estimates; reserve headroom for the model response.
About AI Context Window Calculator
The AI context window calculator shows how much of a model’s context window your prompt consumes and how much room remains. Pick a model, the window sizes for popular AI models are built in, or enter a custom window, then set your system prompt tokens, input/conversation tokens and the output tokens you reserve for the response.
A usage bar visualizes the split between system, input, reserved output and free space, with exact used and remaining counts. Enter the typical token size of a document or message and the calculator tells you how many more items of that size still fit, or by how many tokens you are over the limit.
It answers the everyday RAG and chatbot questions: how many support articles fit alongside the system prompt, or when a conversation history must be trimmed. The tool is free and instant; token figures are estimates, so keep sensible headroom for the model’s reply.
How to use AI Context Window Calculator
- Select a model to load its context window, or enter a custom window size in tokens.
- Enter your system prompt tokens and the input or conversation tokens.
- Set the output tokens you want to reserve for the model’s response.
- Optionally enter the tokens per document or message to see how many items fit.
- Read the usage bar, the used and remaining counts, and the fit or over-limit verdict.