Internet speed explained: what Mbps really means

The three numbers on a speed test

• Download speed: how quickly data reaches you. This matters for streaming, browsing and downloading apps.
• Upload speed: how quickly you send data out. This matters for video calls, sending large files and backing up photos to the cloud.
• Ping (latency): the delay, in milliseconds, for a tiny message to go out and come back. Low ping makes video calls and online games feel smooth.

Think of a motorway. Speed in Mbps is how many lanes there are: more lanes, more traffic at once. Ping is how long the journey takes, however many lanes there are.

Bits, not bytes

Speeds are measured in megabits per second (Mbps) or gigabits per second (Gbps). File sizes are measured in megabytes (MB). One byte is eight bits, so divide by eight to estimate download time. A 100 Mbps line can download about 12 MB per second at best. Our guide Bits, bytes, GB and TB explains the units.

How much speed do you actually need?

These are rough, everyday guides rather than exact rules:

The key is to add up what happens at the same time. A family where two people stream, one is on a video call and one is gaming needs more than a single person who mostly browses. For many homes, a plan somewhere between 50 and 150 Mbps is plenty. Upload speed matters more than people expect if you work from home.

Why you rarely get the advertised speed

• Wi-Fi loses speed through walls and over distance. A cable plugged into the router usually shows the true line speed.
• Busy times, such as evenings, can slow shared networks.
• Old devices may not support the latest, fastest Wi-Fi.
• "Up to" speeds in adverts are the best case, not a promise. Check the minimum speed in your contract.

Our guide Wi-Fi basics explains how to improve coverage at home.

Try this: test properly

1. Pause big downloads and streams in the house.
2. Run a speed test on a laptop plugged into the router with a cable, if you can.
3. Run it again on Wi-Fi next to the router, then in the room where it feels slow.
4. Compare the results. If the cable test is fine but Wi-Fi is slow, the problem is coverage, not your provider.

You can also use our bandwidth calculator to see how long a file of a given size will take.

When speed is not the real problem

Sometimes the connection is fast, but things still feel slow. A struggling old laptop, a browser with dozens of open tabs, or a website that is busy at its end can all look like "slow internet". If one site is slow but others are fine, the problem is probably that site. If everything is slow on one device but fine on another, look at the device before you call your provider.