# Bandwidth and latency

> How much data fits per second, and how long each trip takes. Two different things.

- Level: Basic
- Topics: Networks
- URL: https://tidbit.legios.com.ar/bandwidth-and-latency/
- In Spanish: [Ancho de banda y latencia](https://tidbit.legios.com.ar/es/bandwidth-and-latency/)

**Bandwidth** is how much data a connection can move per second, measured in megabits per second (Mbps) or gigabits (Gbps). **Latency** is how long a single piece of data takes to go from you to the other end and back, measured in milliseconds (ms) and often called **ping**. A connection can have lots of one and little of the other, and they feel very different.

Downloading a movie or streaming in 4K needs bandwidth: the pipe has to be wide. A video call, an online game or just clicking around a site needs low latency: each action waits for a round trip, and 200 ms of lag is noticeable even on a gigabit line. Latency is mostly physics and distance: light in a fiber takes roughly 100 ms to cross the Atlantic and come back, and every router on the way adds a bit more. That is why a CDN puts copies of content near you.

When the internet feels slow, ask which one it is. A page that takes a moment to start loading but then arrives all at once is a latency problem (far server, satellite link, overloaded Wi-Fi). A video that keeps buffering is a bandwidth problem (too many devices, a small plan, a weak Wi-Fi link). Internet plans advertise bandwidth; they almost never mention latency.

## An analogy

A highway. Bandwidth is the number of lanes: how many cars pass per minute. Latency is the length of the trip: even on a ten-lane highway, going to the next city takes an hour.

## Keep in mind

- Bandwidth: Mbps, how much per second. Latency: ms, how long each trip takes.
- Streaming and downloads need bandwidth; calls, games and clicks need low latency.
- Distance sets a floor on latency; nothing beats the speed of light, so CDNs move content closer.
- More bandwidth does not fix lag.

## Go deeper

- [What is latency? (Cloudflare)](https://www.cloudflare.com/learning/performance/glossary/what-is-latency/)
- [What is bandwidth? (Cloudflare)](https://www.cloudflare.com/learning/network-layer/what-is-bandwidth/)
- [Latency (MDN glossary)](https://developer.mozilla.org/en-US/docs/Glossary/Latency)

## Related terms

- [Ping](https://tidbit.legios.com.ar/ping/): A tiny "are you there?" message that tests a connection and times the reply.
- [Display resolution](https://tidbit.legios.com.ar/display-resolution/): How many dots, or pixels, make up a screen's image: more dots, finer detail.
- [Router](https://tidbit.legios.com.ar/router/): The box that connects your devices to each other and to the internet.
- [CDN](https://tidbit.legios.com.ar/cdn/): Copies of a website kept on servers around the world, close to whoever asks.
- [Internet](https://tidbit.legios.com.ar/internet/): A worldwide network of networks that lets any connected device reach any other.
- [Server](https://tidbit.legios.com.ar/server/): A computer whose job is to answer requests from other computers, all day, every day.
- [Wi-Fi](https://tidbit.legios.com.ar/wi-fi/): Networking over radio waves: the internet without the cable, within a few rooms.