What is the difference between RPM and TPM?

RPM is the maximum number of requests per minute you may send; TPM is the maximum number of tokens per minute you may process. Providers enforce both at once, so your real throughput is limited by whichever ceiling you hit first. A high RPM is useless if your large prompts saturate the TPM budget.

Why does the calculator apply a safety margin?

Token counts vary per request and clocks drift, so running at exactly 100% of your limit guarantees occasional 429 errors. The default 90% safety margin leaves headroom for variance and bursty traffic while keeping throughput high. Lower it if your workload is very predictable.

How does request size change my effective rate?

Your effective rate is the lower of the RPM ceiling and TPM divided by tokens-per-request. Small requests are RPM-bound, large requests are TPM-bound. The calculator shows which constraint binds so you know whether to shrink prompts or request a higher RPM.

What concurrency level should I use?

Concurrency is roughly your safe RPM multiplied by the average request latency in minutes. The tool estimates a safe number of parallel in-flight requests from your sustainable rate so you saturate the limit without overshooting it. Pair it with exponential backoff for safety.

Does staying under the limit guarantee no 429s?

It makes them rare, not impossible. Token estimates can be off, other clients may share the quota, and providers sometimes apply burst limits. Always keep exponential backoff and Retry-After handling in your client even when your average rate is well under the ceiling.

LLM Rate Limit Calculator

Hitting 429 errors means you are sending requests faster than your tier allows. This calculator turns your RPM and TPM limits plus your typical request size into concrete, safe settings: a sustainable request rate, a concurrency level, and a minimum delay between calls.

How it works

Providers enforce two ceilings simultaneously — requests per minute and tokens per minute — and your real throughput is bounded by whichever you hit first:

RPM-bound rate = your RPM limit.
TPM-bound rate = TPM limit ÷ tokens per request.

The calculator takes the smaller of the two, applies a safety margin (default 90%) for token-count variance and clock drift, and reports the binding constraint plus a safe concurrency estimate and inter-request delay. All math runs locally in your browser.

Tips

If you are TPM-bound, shrinking prompts (trimming history, using retrieval) buys more throughput than a higher RPM ever will. If you are RPM-bound, batching multiple items into one request helps. Keep exponential backoff and Retry-After handling in your client regardless — token estimates drift and shared quotas mean staying under the average rate reduces 429s but never eliminates them entirely.