Free API Bandwidth calculator with clear step-by-step results.
Converts an API's request rate and payload sizes into the bandwidth and monthly egress volume it will actually consume. Both directions of the exchange are counted, header and TLS framing are added as an overhead percentage, and a peak-to-average factor gives the figure you size the link or the rate limit against.
Average throughput
Mbps = RPS x (request KB + response KB) x (1 + overhead) x 8 / 1000
Monthly egress
TB/month = KB per second x 86,400 x 30.4 / 10^9
JSON payload size ignores HTTP headers, cookies, TLS record framing and TCP/IP headers. On small responses that overhead can exceed 30%; on large ones it is closer to 2%.
Decimal - 1 GB = 10^6 KB. Cloud providers bill egress in decimal units, so this matches an invoice rather than a disk-usage tool.