TCP Window Size Calculator

TCP window scaling is an extension that allows window sizes larger than 64 KB. It is required when your BDP exceeds 64 KB, which is common on high-bandwidth or high-latency links. Without window scaling enabled, your throughput will be severely limited regardless of your actual bandwidth.

Packet loss significantly reduces TCP throughput because the protocol must retransmit lost packets and reduce its sending rate. The Mathis formula shows that throughput is roughly proportional to 1 divided by the square root of the loss rate. Even a 1 percent loss rate can reduce throughput to a fraction of the available bandwidth.

MTU (Maximum Transmission Unit) is the largest packet size that can be sent on a network link, typically 1500 bytes for Ethernet. MSS (Maximum Segment Size) is the largest amount of TCP data that can fit in a packet after subtracting IP and TCP headers. For IPv4 with standard headers, MSS equals MTU minus 40 bytes.

Each operating system has different commands for TCP tuning. On Linux, use sysctl commands to adjust tcp_rmem and tcp_wmem values. On Windows, use netsh interface tcp commands to configure auto-tuning levels. On macOS, use sysctl to modify net.inet.tcp settings. The Buffer Tuning tab provides specific commands for each OS.

BBR (Bottleneck Bandwidth and Round-trip propagation time) is recommended for high-latency or lossy networks as it adapts better to real-world conditions. CUBIC is the default on most Linux systems and works well for general use. The Congestion Control tab helps you choose the right algorithm based on your network characteristics and operating system.