How many users a TPM/RPM rate limit can actually serve at once.
TPM and RPM are two ceilings, and only the lower one matters β raising the other is wasted effort. Forecast where traffic pushes you on the API cost forecast calculator, and size the tokens behind each call on the LLM token cost calculator.
The Rate Limit Capacity Calculator figures out how many concurrent active users your application can serve before an API provider starts throttling requests. It does not estimate a dollar cost β it converts your account's two rate ceilings into a headroom number. You enter the token limit (TPM) and request limit (RPM) from your provider, plus your workload shape: tokens per request and requests per active user per minute. The tool divides each ceiling by your per-user demand and reports the lower of the two results, since capacity is set by whichever limit you hit first β token throughput or request count.
The key trade-off is that TPM and RPM run out at different rates, and which one binds depends on your request size. Large prompts or long completions push you against the token limit while request count sits idle; many tiny calls do the reverse. The practical tip is to check which limit the calculator flags as the bottleneck before scaling up. If tokens bind first, trimming context or output length buys more user capacity than a higher request quota would; if requests bind first, batching several operations into one call helps most. Sizing to the binding limit prevents throttled requests and failed responses during traffic spikes.
Providers cap you on both tokens-per-minute (TPM) and requests-per-minute (RPM), and you hit whichever comes first. Small, frequent calls usually hit RPM; large-context calls hit TPM. Your real capacity is the lower of the two, so raising only the non-binding limit changes nothing.
Lift the binding limit β request a higher tier for whichever one caps you, batch or combine small requests to ease RPM, and trim prompt size to ease TPM. Caching repeated context and routing overflow to a second key or model also spreads load beyond a single limit.
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