API Gateway pricing: what to model (requests + transfer)

API Gateway pricing is usually dominated by request charges plus data transfer. Depending on API type and features, you may also see add-ons that matter for production workloads.

API Gateway pricing inputs

Requests/month: from metrics, logs, or RPS conversion.
Response size: average KB to estimate transfer costs.
Effective rates: blend tiers and region pricing.

Where to get the inputs

Requests: API logs, gateway metrics, or analytics. Use a representative week and model peak separately if traffic is bursty.
Payload sizes: average response size from logs or tracing. Use compressed sizes if compression is enabled.
Transfer boundary: which path is billed (internet egress vs internal vs cross-region).

If you only have RPS and average payload size, convert it to GB/month with response size transfer.

What to include in an estimate

Requests/month and your effective $ per million requests
Average response size and the effective egress $/GB for your traffic path
Logging/metrics (if enabled) and downstream costs (Lambda, databases, queues)
Add-ons you use (custom domains, WAF, caching, etc.)

A fast model

Use AWS API Gateway Cost Calculator for a quick request + transfer estimate. Then add any feature-specific line items you rely on.

When transfer dominates

Large list endpoints, exports, file downloads, and “fat JSON” responses can dominate spend.
Retry storms multiply both requests and transfer, even when success traffic is unchanged.
CDN caching in front of the gateway can reduce origin requests and origin transfer for cacheable traffic.

Response transfer Origin egress vs CDN

Common pitfalls

Underestimating transfer by using uncompressed payload sizes.
Retry storms (client retries, SDK retries, timeouts) inflating requests.
Large responses (lists, exports, file downloads) dominating total spend.

Related: API Gateway access logs cost.

Validation checklist

Validate the primary driver with measured usage from a representative window.
Confirm units (GB vs GiB) and request pricing units (per 10k vs per 1M).
Re-check incident windows: retries/timeouts often multiply cost drivers.

Sources

AWS pricing overview: aws.amazon.com/pricing
Use official API Gateway pricing for your region and API type to set effective $/request and $/GB assumptions.

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