API Gateway Rate Limiting Calculator — Model RPS, Burst, and Token Buckets
Calculate token bucket size and refill rate from RPS targets for API gateway throttling. Enter your steady-state requests per second, burst multiplier, and average response time — the calculator outputs the bucket capacity, refill rate, per-minute and per-hour quotas, and concurrent connection estimate. Generates ready-to-paste throttling config for AWS API Gateway, Kong, and Nginx. Free and runs entirely in your browser.
How to Use API Gateway Rate Limiting Calculator — Model RPS, Burst, and Token Buckets
How to Use the API Gateway Rate Calculator:
Load a Preset (Optional): Click any preset to pre-fill all inputs with a common API tier scenario. Free tier shows a low-volume SaaS free plan with generous burst headroom. Standard API covers a typical 100 RPS web API. Pro tier shows a higher-volume paid plan. High-traffic demonstrates a 2000 RPS configuration with tighter burst. All presets can be edited after loading.
Enter Target RPS: The Target RPS is your expected steady-state request rate — the average number of requests your API should serve per second under normal conditions. This becomes the token bucket refill rate. Use your P50 traffic from monitoring or your desired sustained throughput per client tier.
Set the Burst Multiplier: The burst multiplier determines the token bucket capacity: bucket size = Target RPS × Multiplier. A 2× multiplier on a 100 RPS API creates a 200-token bucket, allowing 200 back-to-back requests before throttling begins — after which the bucket refills at 100 tokens per second. Use the quick-select buttons (1.5×, 2×, 3×, 5×) for common values. A 2× multiplier is a sensible default for most APIs.
Enter Average Response Time: The average response time in milliseconds is used to estimate concurrent connections via Little's Law (L = λW). For example, at 100 RPS with a 150ms average response, your API handles roughly 15 concurrent requests. This helps you cross-check whether your backend thread pool or connection pool can support the calculated concurrency.
Set the Window: The window in seconds determines the per-window quota shown in the results. Use 60 for per-minute display, 3600 for per-hour, or a custom value that matches your billing or quota window. The window does not affect the token bucket calculation — it is only used to display the derived quota values.
Click Calculate: Results appear on the right with six key metrics: Refill Rate (tokens per second, equal to target RPS), Burst Size (max token bucket depth), Per Minute and Per Hour derived rates, Per Window quota, and Concurrent Connections estimate. A status badge indicates whether the burst multiplier is tight, balanced, or generous.
Use the Gateway Config Snippets: Switch between AWS, Kong, and Nginx tabs to see a ready-to-paste configuration snippet for each gateway. Click Copy to copy the active snippet to the clipboard.
Common Use Cases:
- API product design: Determine throttle values for each pricing tier (free, pro, enterprise) before configuring your gateway.
- Gateway migration: Re-calculate token bucket parameters when migrating between AWS API Gateway, Kong, and Nginx to ensure equivalent throttling behaviour.
- Capacity planning: Use the concurrent connection estimate alongside your backend thread pool size to verify that rate limits are set below your backend saturation point.
- SaaS quota configuration: Set per-minute and per-hour quota values for SDK rate limiters and quota enforcement middleware.
Tips and Best Practices:
- Set rate limits well below your backend saturation point, not at it. If your service can handle 500 RPS before degrading, set the gateway limit to 300-400 RPS to preserve headroom for retries and traffic spikes.
- A 2× burst multiplier is a safe default for most REST APIs. Use 3-5× for bursty workloads (dashboard loads, mobile app cold starts) where a short burst is expected on startup.
- In Kong with multiple gateway nodes, use the redis policy instead of local to share rate limit counters across nodes. The local policy counts independently per node.
- In Nginx, nodelay serves burst requests immediately without queuing delay. Remove nodelay if you want Nginx to smooth out burst traffic over time instead of rejecting it.
Frequently Asked Questions
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