Should You Choose a 5GB, 30GB, 50GB, or 100GB SIM in Japan?

Do not choose a data allowance by guesswork. Check how much mobile data you used over the last 30 days, determine whether you have Wi-Fi at home, and add a reasonable buffer for busy months. A 5GB plan is usually only suitable for light use; 30GB meets the needs of many typical users; 50GB suits people who watch more video and use social media heavily; and 100GB is worth considering if you often use a hotspot or do not yet have fixed Wi-Fi.

These figures represent usage groups, not a promise that an activity will always consume a fixed number of gigabytes. Video quality, automatic updates, video calls, apps, and the carrier’s method of counting traffic can all change the result.

Quick guide by usage

If a provider offers 10GB, 20GB, or another allowance, place it within the corresponding usage range. The goal is to choose based on actual data, not to force yourself into exactly these four figures.

Step 1: Check how much mobile data your phone has used

On iPhone

Open Settings → Cellular to see usage by app. Pay attention to the statistics period. If it has not been reset for a long time, compare it with your carrier bill or app to identify one recent billing cycle.

On Android

The menu name varies by manufacturer, but it is usually under Settings → Network & Internet/Connections → SIM or Data usage. Select the date range that matches your current plan’s billing cycle.

If you have just arrived in Japan and have no history

Review the data you used in your previous country, then adjust it for your new situation:

• Is Wi-Fi available at home, your dormitory, school, or workplace?

• Is your daily train journey long?

• Will you often use maps and translation apps?

• Will you make frequent video calls to family?

• Will your laptop need to connect through your phone?

You may use more data than usual during your first month in Japan because you will frequently open maps, translate text, search for housing, download documents, and communicate with others.

Step 2: Find the apps consuming your data

Video is often the largest category, but it is not the only cause. Check for:

• Video and social media apps that autoplay clips.

• Photo backups to the cloud over mobile data.

• Operating system or game updates.

• Long video calls.

• Hotspot use for a laptop, tablet, or friends.

• Work-file synchronization.

• Apps running in the background.

Before buying a larger plan, you can disable autoplay, restrict backups to Wi-Fi, and download content before going out. However, do not cut usage so aggressively that it interrupts work or important communication.

Step 3: Confirm that Wi-Fi is actually ready

“I have Wi-Fi at home” only helps if the connection is active. Someone who has just moved may be waiting for fiber installation, may not have received a home router, or may find that shared dormitory Wi-Fi is unstable. During that period, a higher-capacity SIM or temporary Pocket Wi-Fi may be more practical.

If your home Wi-Fi is stable and your company or school also provides a network, 5–30GB is more likely to be enough. If your phone is the main connection for your laptop, evaluate 50–100GB together with the plan’s tethering conditions.

Step 4: Check what happens after you use all your data

Plans differ in more than the number of gigabytes. Read the following conditions:

• Is the connection stopped after the allowance is used, or is the speed only reduced?

• Is the reduced speed sufficient for messages and maps?

• Can you purchase extra data, and in what increments?

• Does unused data roll over to the next month?

• Does the plan automatically move to a higher tier or charge extra?

• Does tethering share the same allowance, and is it separately restricted?

• Does an “unlimited” plan have a fair-use policy or traffic management during congestion?

A 30GB plan with a clear top-up mechanism can sometimes be safer than a 50GB plan with complicated cancellation conditions.

When should you choose 5GB?

5GB may suit you if you:

• Mainly use messaging, email, maps, and news.

• Have stable Wi-Fi at home and at work or school.

• Rarely watch video over mobile data.

• Do not use your phone as a hotspot for a laptop.

The greatest risk is your first month after arriving or a month when you move home. Your needs can rise sharply during those periods. Check the price of additional data before deciding.

When should you choose 30GB?

30GB is a reasonable starting point for many people who use their phone every day but still have Wi-Fi at home. It often suits daily social media, music streaming, moderate video viewing, and occasional video calls.

If you watch video for a long time on the train every day or frequently share your connection with a computer, 30GB can run out quickly.

When should you choose 50GB?

50GB is suitable when your phone plays a larger role in daily life: frequent video viewing, many video calls, mobile work, or occasional hotspot use. It can also be a temporary option while waiting for home internet installation.

Check the tethering allowance. A plan labeled 50GB does not necessarily apply the same allowance and conditions to every type of use.

When should you choose 100GB?

100GB is worth considering if you do not have fixed internet, regularly connect a laptop through a hotspot, or need internet for long periods outside. However, a 100GB SIM does not automatically replace fiber in every situation. Signal strength, latency, upload speed, phone battery, and traffic-management policies can still affect your work.

If several people will share the connection or stream high-quality video continuously, compare the total cost with Pocket Wi-Fi, Home Wi-Fi, and fiber internet.

Hotspot use: the most underestimated part of your consumption

A hotspot is a common reason why a plan that seemed sufficient runs out early. When a laptop connects through your phone, all of the laptop's traffic is deducted from your SIM allowance, including background activity you did not deliberately start.

There are three ways to share a connection, not only Wi-Fi

Google's Android documentation describes three ways to share a mobile connection: a Wi-Fi hotspot (Wi-Fi アクセス ポイント), USB tethering (USB テザリング), and Bluetooth tethering (Bluetooth テザリング). On an Android phone all three are in the same place: swipe down from the top of the screen, then touch and hold the hotspot icon.

Google also notes that tethering an Android device to a Mac over USB is not supported. If you use a Mac, plan for the Wi-Fi or Bluetooth option in advance instead of assuming that a USB cable will always work.

Carriers may set separate limits or charge extra

Google states that, depending on the carrier, sharing a connection may be limited or may incur an additional fee. This is why the tethering terms have to be read as a separate item, not inferred from the number of gigabytes printed in an advertisement. A plan with a large allowance can still come with a tethering limit lower than the data you use on the phone itself.

Remember to plug in while sharing your connection

Google recommends keeping the device connected to power while sharing a connection. This is worth noting if you intend to use your phone in place of a home router: battery and heat are practical limits that sit outside the allowance figure.

Measure one real working session before upgrading

Before moving up to the 100GB group for hotspot reasons alone, record your usage before and after one working session with a laptop connected through your phone. A number measured from your own habits is more reliable than any general estimate, and it sometimes shows that the 50GB group is already enough.

A practical formula for choosing your allowance

1. Take your highest monthly usage from the last three months.

2. Exclude an unusual month only if you are certain it will not recur.

3. Add new needs in Japan: maps, translation, video calls, and hotspot use.

4. Add a moderate buffer.

5. Check whether you can change plans the following month.

For example, if your normal usage is 18–22GB, you have home Wi-Fi, and you do not use a hotspot, a 30GB range may be more appropriate than 50GB. If your history is already 35–40GB, choosing 30GB and repeatedly buying add-ons will often be inconvenient.

Do not overlook calls and SMS

The data allowance does not answer whether you need a Japanese phone number. When comparing plans, check:

• Does the plan include calls and SMS, or is it data-only?

• Are calls charged per minute, included in an add-on, or made through a separate app?

• Can the number receive verification SMS messages?

• Can you keep the number when switching carriers through MNP?

• Is an eSIM or physical SIM suitable for your device?

A cheap data-only plan may not suit you if you need to receive calls from a real-estate agent, employer, or delivery company.

Common mistakes

Choosing based on an advertisement that says “use freely”

Read the detailed conditions. A large allowance does not mean the connection will always be fast at every time and location.

Forgetting hotspot data

A laptop may update its system, synchronize cloud files, and download large files in the background. A single work session can use more data than expected.

Buying 100GB even though Wi-Fi is available most of the time

Unused data adds no value if it does not roll over. Compare the total cost difference over a full year.

Choosing 5GB and buying extra data every month

If you regularly exceed the allowance, a cheap base plan may not have the lowest total cost.

Not checking coverage

A large allowance does not help if the signal is weak at home, work, or along your main travel route.

Frequently asked questions

How many gigabytes does one hour of YouTube use?

There is no single fixed figure. Usage depends on resolution, frame rate, encoding, and app settings. Use your phone’s statistics to measure your actual viewing habits.

Is 30GB enough for an international student?

It can be enough if the dormitory or school has Wi-Fi and you do not watch too much video over mobile data. Someone who makes frequent video calls, spends a long time on trains, or has no Wi-Fi may need more.

Can 100GB be used as home Wi-Fi?

It can work in some situations, but you must check tethering, signal, usage limits, number of devices, and stability. For several users or demanding work, compare it with Home Wi-Fi and fiber.

Should I change my plan every month according to my needs?

If the provider allows easy changes without unfavorable conditions, this can be an effective way to optimize costs. Check when the change takes effect.

Can using two SIMs reduce data usage?

Two SIMs can separate calls from data or provide a backup network, but they do not automatically reduce your total data needs. Your device and carriers must support the relevant configuration.

Conclusion

The right allowance is enough for a high-usage month without leaving a large amount unused over the long term. Use your past consumption as the basis, add new needs, and read what happens after the allowance is exhausted. Only then should you compare price, network, and contract duration.

Want to choose a plan based on your needs instead of guessing? NST Connect can use your length of stay in Japan, data needs, call requirements, hotspot use, and usage address to suggest a suitable SIM or Wi-Fi category. Link to the “Find Your Plan” tool only after that page is live.

Related articles

• What’s the Difference Between Voice SIMs, Data SIMs, and eSIMs?

• Pocket Wi-Fi, Home Wi-Fi, or Fiber Internet in Japan: What’s the Difference?

• Which Internet option is best for 3, 6, 12, or 24 months in Japan?

• Canceling a SIM or Wi-Fi in Japan: avoid extra charges

The data ranges in this article are selection guidance, not fixed consumption standards. Check the data and tethering terms in the documentation for each specific plan.