Mbps, MB and GB: internet speed explained

Internet speed is sold in megabits per second, but files are measured in megabytes. A byte is eight bits, and that one fact clears up most confusion.

Bits and bytes

• A bit (small b) is the smallest piece of data. Speeds are counted in bits per second: Kbps, Mbps, Gbps.
• A byte (capital B) is eight bits. File sizes and data packs are counted in bytes: KB, MB, GB.

So to turn a speed in Mbps into megabytes moved each second, divide by 8.

These are best-case times at a steady speed. Our download time calculator works out any size and speed.

Download, upload and why they differ

Download speed is data coming to you: pages, video, app updates. Upload speed is data leaving you: sending photos, video calls, backups, live streaming. Many cable and wireless plans give far less upload than download. Fibre plans are often equal both ways. If your video calls look fine to you but others see you frozen, upload is the weak side.

How much speed do tasks need?

Exact needs depend on the service and the quality setting, and each service publishes its own figures. As a rough guide to scale:

• Messaging, email, music streaming and ordinary browsing need well under 1 to 2 Mbps.
• A video call or standard-definition video needs a few Mbps.
• High-definition video needs several Mbps per screen; 4K needs a few tens.
• Large game and app downloads use as much as you have; more speed only shortens the wait.

What matters at home is the total at the busiest moment. Two 4K televisions, a video call and a console update at the same time need far more than any one of them.

Why your result is lower than your plan

• "Up to": plans state a maximum, not a promise.
• Wi-Fi: walls, distance and neighbours' networks cut speed, most of all on the 2.4 GHz band. A test over cable beside the router shows what the line itself delivers.
• Other devices sharing the line at that moment.
• The device: an old phone or laptop may not manage the full speed of a fast plan.
• Busy hours: evenings are slower on crowded networks.
• The far end: a slow server cannot send faster than it can.

If a cable test beside the router, at a quiet time, with other devices off, is far below the plan on several days, you have good grounds to complain to the provider. Note the dates and figures.

Data packs: GB per day

Mobile packs are sold by volume, not speed. To see how long a pack lasts, think in megabytes per hour. A steady 1 Mbps stream uses 450 MB an hour (1 ÷ 8 × 3,600 seconds). A 5 Mbps video therefore uses about 2.25 GB an hour. Lowering video quality in the app's settings is the single biggest saver.

Speed is not everything

A connection can be fast and still feel bad in games and calls if its delay is high or uneven. That is measured by ping, latency and jitter, and you can try our response time test.