GPT Calculator exists to answer a very practical pre-flight question: how much will this prompt cost, and how many tokens does it contain? Rather than guessing, you paste your prompt text into a single field, select the target model from a dropdown, and submit. The tool returns a token count and a cost estimate derived from that model's published per-token rates, so you can budget, trim, or restructure a prompt before committing it to an API call.
The model selector covers the widely used families: GPT-4, GPT-3.5, and the legacy GPT-3 Ada and Davinci variants. Because tokenization differs between model generations, calculating against the right model matters for accuracy, and the tool keeps those options explicit. There is also a documented API, which lets developers wire token counting and cost estimation directly into their own scripts, dashboards, or CI pipelines instead of visiting the page each time.
It is worth being clear about provenance: GPT Calculator describes itself as an independent archived tool and states it is not affiliated with or endorsed by OpenAI, and that all trademarks belong to their owners. That makes it a handy third-party estimation aid rather than an authoritative billing source — treat the numbers as a close guide, since provider pricing and tokenizer behavior can change over time. The site is free to use, needs no account, and complements the small blog that accompanies it.