The answer to "how many GB?" is already on your phone. iPhone: Settings > Screen Time. Android: Settings > Digital Wellbeing. Both show how many minutes a day you spend in each kind of app. Put those minutes in below and we will do the rest.
iPhone: Settings > Screen Time > See All App & Website Activity > Week tab, "Categories" section. Android: Settings > Digital Wellbeing & parental controls > Dashboard. If you would rather not look them up, start from one of the presets below and adjust.
How much internet will you use?
An estimate based on averages, with a 20% safety margin already included.
How the estimate works
Each kind of usage has a fairly stable hourly cost on a phone screen: video streaming ~700 MB/h, social feeds ~350 MB/h, video calls ~450 MB/h, music ~100 MB/h, browsing ~60 MB/h, messaging ~15 MB/h, navigation ~5 MB/h. We multiply your minutes by those rates.
- We subtract the share of the day you spend on Wi-Fi - data used at the hotel or a café never touches your plan.
- We add ~50 MB a day of background traffic that flows even when you do nothing.
- If photo backup is on we add ~250 MB a day; on its own, that single item drains most plans.
- We add a 20% safety margin: travel usage runs higher than usage at home, and running dry mid-trip is the expensive kind of mistake.
The result is based on averages. High-resolution video, large app updates or constant tethering can multiply consumption. If in doubt, take the next size up - or start small and top up along the way.