ChatGPT context window calculator
Estimate how much source context you can give ChatGPT while leaving room for instructions and a useful answer.
GPT-4.1 budget planner
GPT-4.1 supports a ~1M-token context window and up to 32K output tokens. OpenAI's current flagship text model.
Source: OpenAI documentation. Last reviewed 2026-06-05.
Frequently asked questions
What models does this calculator cover?
It shows GPT-4.1 (~1M tokens), GPT-4.1 mini (~1M tokens), and GPT-4o (128K tokens). Select the variant you are using to plan your context budget.
Can I use this for ChatGPT Projects?
Yes. Use it to estimate whether your source text, prompt, and expected answer have enough room before adding files to a project or chat.
Is this an exact OpenAI tokenizer?
No. It is a planning calculator. For exact API tokenization, use OpenAI's model-specific tokenizer tooling.
Can Riflet prepare ChatGPT context files?
Yes. Riflet exports text or Markdown bundles that can be pasted or uploaded into ChatGPT when the product surface supports it.