If you buy too little, you'll have to worry about running out of data in the middle of the road. If you buy too much, you'll waste money. There's no right number for everyone, but you can get a pretty close estimate with just a few questions about how you use the internet. This article goes from consumption by activity, to suggestions by days, and an important constraint that many people overlook.
The numbers below are general estimates, vary by video quality and usage habits, but are enough to give you an idea of what consumes data.
Take the daily rate above and multiply it by the number of days to get a rough estimate for the whole trip, calculated by basic usage group:
If you belong to the group that uses a lot, choose a package one step larger or consider buying more when needed.
Here's where many people miss: expiration dates are hard constraints. A package with a lot of data but a term shorter than the number of travel days will still not use the entire trip. Choose a package with a limited number of trip days or more first, then consider the capacity.
Tip: If you're still wondering, just choose a little more than the estimate for peace of mind. Missing data mid-trip is much more annoying than having a little extra.
For most travelers — checking Google Maps, texting, checking trains, translating, and moderately surfing the internet — 1GB per day is comfortable enough. You only hit the limit if you watch a lot of videos or make long video calls.
Each hour of HD video can consume more than 1GB. If you watch YouTube or make video calls home every night, consider adding about 1–2GB per day, or choose a higher capacity plan from the start for peace of mind — see Japanese eSIM plans by capacity.
You can buy a new package and install it on top to continue using it. Don't turn on data roaming on your Vietnam SIM to fight the fire, because roaming charges are very expensive.
You should only choose unlimited if you actually watch a lot of videos or live streams every day. For normal travel needs, GB packages are often cheaper but still have plenty of capacity.
The data estimate does not need to be absolutely accurate, it just needs to be close enough to not miss out mid-way. On the page shibaSIM's Japanese eSIM plan there is a suggestion tool: you enter the number of days and describe usage, the system estimates GB and suggests a package that covers both data and expiry date. If your trip is for a week, read more How many GB should you choose for a 7-day Japanese eSIM package.
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