Context Window Calculator
Calculate how much of an AI model's context window your prompts use. Plan token budgets for GPT-4, Claude, Gemini and compare capacity across models.
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Plan Your LLM Context Usage
LLM context windows determine how much information you can include in a single prompt. Our Context Window Calculator helps you plan token budgets, visualize usage, and compare capacity across GPT-4, Claude, Gemini, and other models.
What Is a Context Window?
A context window is the maximum number of tokens an LLM can process in a single request—including your prompt and the model's response. GPT-4o has 128K tokens, Claude 3 has 200K, and Gemini 1.5 Pro leads with 1M tokens. Exceeding the limit causes truncation or errors.
Context Usage Formula
Available Tokens = Context Window - System Prompt - User Input - Expected OutputWhy Calculate Context Window Usage?
Prevent Truncation
Exceeding the context window causes your prompt or response to be cut off, losing critical information. Calculate usage before sending expensive API calls.
Budget Token Usage
System prompts persist across conversation turns, eating into available space. Plan your token budget to leave room for user input and responses.
Choose the Right Model
Small context windows (8K-32K) suit simple queries. Long documents and code analysis need 128K+. RAG applications may require Gemini's 1M context.
Optimize Costs
Larger context windows often mean higher costs. Use the minimum context size that fits your use case to minimize API expenses.
How to Use This Calculator
Frequently Asked Questions
The API will either return an error, truncate your input from the beginning, or truncate the response. This can cause loss of critical context, broken code, or incomplete answers. Always leave a safety buffer.