Round-trip time (RTT) is the duration, measured in milliseconds, from when a browser sends a request to when it receives a response from a server. It's a key performance metric for web applications and one of the main factors, along with Time to First Byte (TTFB), when measuring page load time and network latency.

Round Trip Time (RTT) is a fundamental metric in networking that measures the total time, in milliseconds, it takes for a signal to travel from a source to a destination and then back again. It acts as a primary indicator of network latency and responsiveness. When a computer sends a "ping" or a data packet, the RTT includes the propagation delay (time spent traveling through fiber or copper), processing delay at routers, and queuing delay during periods of high traffic. In 2026, as high-frequency trading and cloud gaming become more prevalent, maintaining a low RTT is critical. Factors like physical distance, the number of "hops" between nodes, and the type of medium (e.g., satellite vs. terrestrial fiber) all influence this value. A high RTT typically results in noticeable "lag" or delays in communication. Network engineers use RTT to diagnose bottlenecks and optimize routing protocols, ensuring that data packets take the most efficient path possible to minimize the "echo" time across the global internet infrastructure.