# API Rate Limit Throughput Calculator

> Find your real API throughput from a requests-per-minute limit, concurrent requests and latency, the concurrency needed to reach the limit, and batch time.

Category: Software, cloud & AI · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/api-rate-limit-throughput-calculator

Your throughput is the lower of two ceilings: the provider’s rate limit, and what your concurrency allows (concurrent requests ÷ latency). Little’s law links the two.

Also called: Requests per minute calculator, API concurrency calculator.

## Inputs
- Rate limit (unit requests/min; default 600)
- Concurrent requests in flight (default 5)
- Average latency per request (unit ms; default 1000)
- Requests to process (default 3000; optional)

## Results
- Achievable throughput
- Per second
- Ceiling set by concurrency
- Limiting factor
- Concurrency needed to reach the limit
- Time for the batch

## Formula

```
Concurrency ceiling = Concurrency × 60,000 ÷ Latency ms;  Throughput = min(Rate limit, Concurrency ceiling);  Concurrency needed = ⌈Rate limit × Latency ms ÷ 60,000⌉
```

Where:
- Latency ms: average time from sending a request to receiving the full response
- Rate limit: requests per minute allowed

## Worked example
1. 5 requests in flight, each taking 1 s: 5 × 60 = 300 per minute.
2. That is below the 600/min limit, so concurrency is the bottleneck; 600 × 1 s ÷ 60 = 10 concurrent requests would reach the limit.
3. 3,000 requests at 300/min take 10 minutes.

**Result:** With 5 concurrent 1-second requests you reach 300 requests a minute, half the 600 limit; double the concurrency to use it all.

## What the result means

If concurrency is the bottleneck, add parallel workers up to the needed figure. If the rate limit binds, more concurrency only causes 429 errors: batch requests, cache results, or ask for a higher limit.

## Assumptions and limits
- Latency stays the same as concurrency rises.
- The rate limit is enforced smoothly over the minute.
- Token-based limits (such as tokens per minute on LLM APIs), burst limits and retries are not modelled.

## Questions

### What is Little’s law?

In a stable system, items in progress = arrival rate × time each spends in the system. Here: concurrent requests = requests per second × latency in seconds.

### Should I run at exactly the limit?

Aim slightly below it, for example 80–90%, with back-off on 429 responses, because latency and limits fluctuate.

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Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/api-rate-limit-throughput-calculator