Latency
Latency is the time a packet needs to travel to a destination and back, usually measured in milliseconds with ping.
What latency is
Latency is delay. In network terms it is usually reported as round-trip time: how long it takes for a small packet to reach a destination and for the reply to come back. Ping measures it with ICMP echo requests; browsers measure a comparable value by timing a tiny HTTP request. Values are given in milliseconds. A wired connection to a server in the same city is typically under 10 ms; crossing a continent takes 30 to 80 ms; an intercontinental path takes 100 to 300 ms, limited by the speed of light in fiber and the number of routers along the way.
Latency and bandwidth are independent. A connection can move hundreds of megabits per second and still have 200 ms of latency, which is why a fast line can feel slow for interactive work.
What adds to it
- Distance: roughly 5 ms per 1,000 km of fiber, each way.
- Each router and switch on the path, usually a fraction of a millisecond, more when the device is busy.
- Queuing when a link is saturated, which is what makes latency spike during a large download. The variation this causes is jitter.
- The last mile: cable and DSL add a few milliseconds, cellular adds tens, satellite adds hundreds.
- Any proxy, VPN, or tunnel, since the packet has to travel to the exit and back in addition to its real route.
Why it matters
For calls, games, and remote desktops, latency decides whether the connection is usable. For proxy and VPN users it is also a location check: the round-trip time to a server is bounded below by the physical distance, so an address that claims to be in one city but answers a nearby server with 180 ms of delay is probably somewhere else. Our tools do not score this signal, because it needs measurements from a known location, but fraud systems with servers in several regions use it.
How to check
The ping tool measures round-trip time from our measurement node to any host and reports minimum, average, maximum, loss, and jitter. The speed test measures the latency between your browser and our server before it measures throughput, which reflects your own connection including any proxy in the path. Traceroute shows where along the route the delay accumulates.
A common misconception
Low latency to one server says nothing about another. Latency is a property of a path, not of a connection, so test against the destination you actually care about.