TCP Window Size Calculator

Size the TCP receive window from link rate and RTT via the bandwidth-delay product.

Link rateRTT (ms)

Window625000 B (610 KiB)

ScalingRequired (> 65535 B) — enable window scaling

How to read the result

Window (bytes) = rate × RTT / 8. Windows above 65535 need RFC 7323 window scaling.

Example

100 Mbps × 50 ms → ~625 KiB window

FAQ

What is BDP?

Bandwidth-delay product: the bytes that must be in flight to keep the link fully utilized.

When is scaling needed?

Whenever the BDP exceeds 65535 bytes — true for most high-speed or high-RTT paths.