How much mobile data do I need?
Almost nobody knows, because the number is quoted once when you sign up and never mentioned again. Here is what each allowance size actually covers, and how to check what you use.
Start with the number you already have
Before estimating anything: your phone has been counting. Android reports mobile data use under network settings, iOS under mobile service, and your network’s own app shows the last few months billing period by billing period.
That record beats any estimate, including ours, because it is a measurement rather than an inference from how many hours you think you spend on things. Look at the highest month in the last year rather than the average — the worst month is the one an allowance has to fit.
What each allowance actually covers
These are rough shapes rather than promises, and they assume home and work Wi-Fi are doing the heavy lifting, which for most people they are.
1–2 GB. Messaging, email, maps, music on the commute, and browsing. No video to speak of. This is genuinely enough for a lot of people and it is sold as though it is enough for nobody.
3–5 GB. The above plus perhaps half an hour of video a day, or a commute spent scrolling a feed that autoplays clips.
8–15 GB. Video is now a daily habit rather than an occasional one, or you are out of the house enough that Wi-Fi is doing less of the work than it does for most people.
20–50 GB. Either a lot of video on the move, or tethering a laptop regularly, or no usable broadband at home.
Unlimited. Worth it when the phone genuinely is the household connection, or when tethering replaces broadband. Worth much less than it sounds when it is bought as insurance against a number nobody has ever looked at.
Why the honest answer is a range
An hour of navigation uses about 5 MB. An hour of 4K video uses around 7,000 MB. Both are “an hour on your phone”. Even within one activity the spread is wide: an hour of social media is roughly four times heavier when video autoplays than when it does not.
That means any estimate built from hours has real uncertainty in it, and a calculator printing “43.7 GB” is hiding that rather than resolving it. Our mobile data calculator carries the low, typical and high figures through separately and shows you the band that comes out.
Buy for a typical month, not the worst one
There is a bias worth naming here, because every site that sells plans has it: sizing you from the top of your range always recommends a bigger allowance, and bigger allowances pay better. It is also not obviously wrong — nobody wants an overage charge.
The honest way to hold it is that headroom has a price, and you should know what you are paying for it. If a 10 GB plan and a 30 GB plan differ by £6 a month, that is £144 over two years to cover months that may never come. Check your actual highest month before deciding that is worth it.
It is also worth knowing what your network does when you run out. Some cut you off until you buy more, some slow you to a crawl, and some charge by the gigabyte. Those are very different risks and they change how much headroom is worth buying.
The things that make last month unrepresentative
A holiday, a stretch of broadband trouble at home, a new phone restoring itself from a backup over mobile data, or a month spent tethering a laptop. Any of these can double a month and none of them says anything about what you normally need.
Look at several months before concluding anything, and if one is an outlier, work out which of these it was.
Before you buy more, try using less
Two settings account for most of the data people cannot explain: video quality on mobile data, and automatic photo backup. Both are free, both are reversible in a tap, and between them they routinely move a month by several gigabytes.
How to reduce mobile data usage covers those and the rest, in order of how much they save. It is worth a month of trying before paying for a larger allowance permanently.