The 15GB plan looks reassuring. You probably don't need it.
I tracked my data usage across a two-week trip through Japan and Thailand last year. Here's what I actually used: 4.1GB. That included Maps navigation daily, WhatsApp calls home every other evening, Instagram stories, and one evening of YouTube on a slow train. No Netflix, no heavy video calls.
Most casual travellers land somewhere between 1.5GB and 5GB per week. Here's why.
What actually uses data
Google Maps: About 5-10MB per hour of active navigation. Light. And if you download offline maps beforehand, navigation itself uses zero data - it only calls home for live traffic updates.
WhatsApp messages: Negligible. Text messages are a few kilobytes each. Voice messages are tiny. Even a 30-minute voice call uses under 15MB.
Instagram and social: This depends entirely on how much you scroll. Casual checking - posting a few photos, viewing stories - is maybe 100-200MB per day. Heavy scrolling with videos autoplay can burn through 1GB in an afternoon.
Email: Nearly nothing unless you're downloading large attachments.
Video calls (WhatsApp, FaceTime): About 300MB per hour at standard quality. A 20-minute call home is around 100MB. Not huge, but they add up if you're calling daily.
Streaming video (Netflix, YouTube): This is the data killer. Netflix at standard quality uses about 1GB per hour. YouTube at 1080p is similar. One episode of something is 700MB-1GB. If you're streaming nightly in your hotel, your data needs jump significantly.
Real usage examples by trip type
City break (3-4 days, one city): You'll use Google Maps a lot the first day as you figure out the layout, then less as you get oriented. Expect 1-2GB total. A 3GB plan gives you plenty of room.
Beach holiday (7 days, mostly resort): You're on resort Wi-Fi most of the time. Mobile data is just for the odd taxi ride or restaurant lookup. 1-2GB for the whole week. The smallest plan your provider offers is probably fine.
Backpacking (2-3 weeks, multiple cities): More Maps usage, more hostel booking lookups, probably more social media posting. 5-8GB total. Go for a 10GB plan for peace of mind.
Business trip (5 days): Email, Slack, maybe a couple of video calls when hotel Wi-Fi flakes out. 3-5GB depending on how much you rely on mobile data vs hotel Wi-Fi.
Road trip (10-14 days): Navigation runs constantly. Streaming music in the car. Looking up restaurants and fuel stops. This is the heaviest use case - expect 8-12GB. Get a bigger plan or be prepared to top up.
So what plan should you get?
For a week-long trip, mostly casual use: 3GB is fine. Honestly, I'd say the 3GB plan is adequate for probably 70% of holiday travellers who aren't streaming video. 5GB gives comfortable headroom.
Two weeks of similar usage: 5-7GB. The 10GB plans are good if you'll be doing video calls daily or posting a lot of content.
If you're streaming video in the hotel every night: add 5-7GB on top of whatever you'd normally use. Skip the unlimited plan unless you're genuinely going to use it - they're usually more expensive and the speed often gets throttled after a certain amount anyway.
Check plans at getesimonline.com - they break down data allowances by destination so you can pick the right size without overpaying.
Destination matters more than you think
Some destinations naturally push you to use more data than others. Japan and South Korea have complex public transit systems that keep you checking Google Maps constantly. US road trips mean hours of navigation. In contrast, a resort holiday in the Maldives or a beach week in Crete barely uses any mobile data because you're on resort Wi-Fi most of the time.
Cities with good signage and walkable layouts (Barcelona, Amsterdam, Florence) mean less Maps usage. Cities with sprawling layouts and car-dependent infrastructure (Los Angeles, Bangkok, Dubai) mean more. Factor in the type of trip, not just the length, when picking your data plan size.
Tips for using less
Download offline maps for everywhere you're going before you leave home. Turn off auto-updates in the App Store and Play Store. Set WhatsApp media downloads to Wi-Fi only. Use hotel/cafe Wi-Fi for anything data-heavy and treat your mobile data as a backup. These habits alone can halve your data usage.
The Netflix trick
If you want to watch shows in your hotel, download episodes on your home Wi-Fi before you fly. Netflix, Disney+, Amazon Prime, and YouTube Premium all let you download content for offline viewing. A downloaded Netflix episode takes up about 250-500MB of phone storage but uses zero mobile data. This single tip can save you 5-7GB over a two-week trip.
Photo uploads eat more than you think
If you're backing up photos to Google Photos or iCloud, each photo is 3-8MB. Take 50 photos a day (easy on holiday) and that's 150-400MB daily just on backups. Turn off automatic photo backup on mobile data - do it on Wi-Fi at your hotel each evening instead.
The connectivity tips guide has more detail on managing data efficiently abroad.