Japan Travel Guide: SIM, Data and Getting Online
What you will actually connect to
Japan has three national networks and travellers reach two of them: KDDI and SoftBank. Both run 5G in every major city, and both are dense enough that you will rarely see a bar drop in Tokyo, Osaka or Kyoto.
Typical download speed across Japan is 74 Mbps, and 21 Mbps at the busiest moments. That busy hour figure matters more than the headline: it is what you get on a crowded platform at Shinjuku at six in the evening.
Japan runs 5G standalone as well as non standalone, which is rarer than the marketing in most countries suggests. In practice it means the 5G icon on your phone in Tokyo is usually telling the truth rather than describing a 4G core with a 5G radio bolted to it.
How much data you need
A city trip in Japan runs around 700 MB to 900 MB a day if you are using maps constantly, translating menus and posting photographs in the evening. Train wifi is unreliable and hotel wifi is usually good.
The safest way to buy is slightly under, then top up. A top up takes about ten seconds and, on a wallet whose gigabytes do not expire, buying short costs you nothing. On an expiring ticket the same decision is a gamble, which is exactly why expiring tickets are sold in sizes that encourage you to overbuy.
- One week, city focused: 5 GB
- Two weeks with day trips: 10 GB
- A month, working remotely: 20 GB or a subscription
What a day in Japan actually costs you in data
| What you are doing | Rough cost | A fortnight of it |
|---|---|---|
| Maps and navigation, two hours a day | 10 MB a day | About 140 MB |
| Messaging, email and train times | 10 MB a day | About 140 MB |
| Translating menus and signs by camera | 60 MB a day | About 840 MB |
| Social with video autoplay, one hour | 300 MB a day | About 4.2 GB |
| One video call home, thirty minutes | 200 MB a day | About 2.8 GB |
Turn off video autoplay and the fortnight lands near 5 GB rather than 8 GB. That single setting saves you more than any plan choice you can make.
The rural gap nobody mentions
Several prefectures are still 4G only, and a handful of mountain areas in Nagano, Gifu and northern Tohoku have real gaps. If your trip includes hiking, download your maps before you leave the station.
Tethering rules also differ between the two host networks. Orbislo tells you which one you are on, which is not information anyone else in this category gives you. Tethering itself is included on every plan at the same allowance as your data, and it is never turned down without a notice on your screen saying so.
Across the whole catalogue, 88 of 197 destinations are not full 5G, so Japan is not unusual in having a gap. It is unusual in how sharp the gap is: the difference between a Tokyo platform and a Nagano valley is larger than the difference between two average countries.
Getting a code sent to you while you are there
A travel eSIM is data only. It has no phone number, so an SMS from your bank has nowhere to land. This catches people out in Japan more than most places, because a lot of ticketing and booking flows want a code.
The free fix is to leave your home SIM active with its data switched off, so calls and texts still arrive on your usual number while the travel line carries everything else. The second fix is wifi calling, which has to be turned on before you fly. The third is to move your bank to app based approval before you leave, so a sign in is confirmed inside the banking app over any data connection instead of by text.
What to do at the airport
Nothing. If you installed before you flew, your data is live while the aircraft is still taxiing. If you are still offline in the terminal, turn airplane mode on, wait ten seconds and turn it off. That clears almost every arrival case.
If it does not, the checklist below is the one support uses, in order. Do not buy a second eSIM at an airport counter until you have worked through it, because the fault is usually a switch on your own phone rather than the product.