Estimate API requests per month (RPS, logs, and metrics)

If your cost driver is per request, you need a defensible requests/month number. The key is to estimate from a measured source (metrics or logs) and include retries and automated traffic.

Quick request count sources

Metrics: CloudWatch request count by stage.
Logs: count log lines for the API stage.
RPS: convert average RPS to monthly volume.

Method 1: use API metrics (best if available)

Use API request count metrics for a representative window (7-30 days).
Sum daily totals, then scale to a month (or take an average day and multiply by 30.4).
Segment by stage/environment (prod vs staging) if they are billed separately in your model.

Tip: use two windows (normal week and peak week) to create a baseline and busy-month range.

Method 2: count from access logs (good when metrics are missing)

Count log lines per day for the API stage you care about.
Exclude synthetic checks if they are frequent and not user-driven.
Keep retries: if they hit the API, they are billable traffic.

Related: API Gateway access logs cost.

Method 3: convert from RPS (fastest early estimate)

Requests/month = avg RPS x 60 x 60 x 24 x days
If you only have peak RPS, apply a duty cycle (e.g., 20% of peak) and validate later.
For bursty workloads, integrate by hour/day instead of using a single average.

API Gateway request estimator RPS to monthly requests API request cost

Method 4: users x actions (useful before you have telemetry)

Estimate daily active users x API calls per user per day.
Split heavy endpoints (search, list, export) into their own call estimates.
Model background workers (sync jobs, webhooks, queue consumers) explicitly.

Common pitfalls

Using peak RPS as an average and overstating cost by 5-10x.
Missing retries and timeouts (they can double or triple traffic during incidents).
Ignoring automated traffic (health checks, bots, cron jobs, integrations).
Mixing environments (prod + staging) when you only want production.

Next: turn volume into cost

Use AWS API Gateway Cost Calculator to translate requests and response size into a monthly request + transfer estimate.

Validation checklist

Cross-check at least two sources (metrics + logs, or metrics + analytics).
Validate the busiest endpoints separately (they often dominate total requests).
Confirm whether the request count includes cached hits (CDN) vs origin requests (API).