Who Is a 300GB/Month Data Plan Best For? How to Check Your Needs

Quick Answer

A 300GB/month data plan is roughly equivalent to about 10GB per day. This amount is only truly worth the money for people who use their phone in place of a fixed home WiFi connection: tethering to a laptop for studying/working, watching HD movies every evening, video calling Vietnam daily, or sharing the connection across 2–3 devices.

If your home or dormitory already has WiFi, your company/school has WiFi, and you mainly use LINE, Facebook, and TikTok while on the train — then you almost certainly won't use up 300GB, and buying a smaller plan will save you much more money. The most accurate way to check: open the data usage stats on your phone, look at the number for the most recent month, then add a 20–30% buffer.

Who this article is for

This article is for foreigners living, studying, and working in Japan who are torn between different SIM/eSIM data amounts. Specifically:

• International students, technical interns, and engineers who have just arrived in Japan, haven't set up a fixed-line connection (hikari) yet, and are considering using a large-capacity data SIM as a replacement.
• People in short-term rentals, share houses, or dormitories where WiFi is slow or unstable during peak hours.
• People who move often or change work sites frequently and don't want to be tied to a 2-year fixed-line contract.
• People working/studying online, joining Zoom or Google Meet calls, or downloading large files on a laptop via tethering.
• People who video call Vietnam every day to see family, or livestream for online sales.
• People currently on a small plan who get throttled every month partway through, and want to know how many GB is actually enough.

If you just want to know "how many GB should I buy?", the Steps to follow section and the GB conversion table below are the parts you should read most carefully.

Cases where this does NOT apply

This article is not meant for the following situations, and buying a 300GB plan in these cases is usually a waste of money:

• You need a Japanese phone number to make/receive calls (for bank account registration, job applications, signing a housing contract, or registering your residence card with a company). A data-only plan has no calling number. In this case you need a voice-calling SIM — that's a different topic.
• Your home already has a stable fixed-line connection. When you're home you use WiFi, so your SIM data is only used when you're out — usually 5–20GB/month is enough.
• You need to share a connection with a whole family of 4–5 people using it continuously. A phone acting as a hotspot all day will overheat, drain the battery, and become unstable. In this case, look into a monthly pocket WiFi or a fixed-line connection instead.
• You're only in Japan for a few weeks (tourism, short business trip). A large monthly plan isn't as economical as a short-term plan.
• You mostly just text, make LINE voice calls, and read news. This group typically uses under 10GB/month.

Steps to follow: check your own data needs in 5 minutes

Don't guess. Your phone has already recorded the data. Follow these 6 steps in order:

1. Open the data usage stats on your device.
   • iPhone: Settings (設定) → Cellular (モバイル通信) → scroll down to "Current Period" (現在までの合計).
   • Android: Settings → Network & Internet (ネットワークとインターネット) → SIM / Data usage (データ使用量) → check the monthly cycle.
2. Check whether this number is reliable. On iPhone, the figure is only accurate if you pressed "Reset Statistics" (統計情報をリセット) at the start of last month. If you don't remember when you last reset it, the number could be a cumulative total over several years — ignore it and move to step 3.
3. If there's no reliable data, measure over 7 days. Press "Reset Statistics" today, go about your normal routine for 7 days, then check the number again. Multiply that number by 4.3 to get an estimated monthly usage. Make sure to pick a normal week, not a long holiday week or a travel week.
4. List out your usage habits by hour/day: how many hours of YouTube, how long you video call, whether you tether to a laptop. Then cross-reference with the conversion table below to add up an estimated figure.
5. Add a 20–30% buffer. Every month brings something extra: iOS/Android updates (2–7GB), downloading a new game, backing up photos to iCloud/Google Photos, or a trip where you use Google Maps constantly.
6. Choose a plan based on your final number, try it for a month, then reassess. If you still have more than half your data left at the end of the month, downgrade to a lower tier the following month.

Conversion table: how much data does 1 hour of use cost?

These are reference consumption levels (they vary depending on the app, network quality, and device settings):

How to read the table: if every evening you watch 2 hours of 1080p movies (about 5GB), plus 1 hour of video calling home (0.4GB), plus some casual browsing (0.5GB) → about 6GB/day → about 180GB/month. Adding a 25% buffer brings that to around 225GB. In this case, a 300GB plan is reasonable. But if you only use 1–2GB/day, that's only about 45GB for the whole month — buying 300GB means paying for data you'll never use.

Who is really a good fit for a 300GB/month plan?

• People using their phone as a replacement for home internet. Tethering a laptop for online classes, watching Netflix on a TV box, downloading files. This group typically uses 150–300GB.
• People whose housing can't have a fixed-line connection installed (landlord won't allow wall drilling, short-term lease, dormitory).
• Households of 2 people sharing one connection, for example a couple who both watch movies in the evening.
• People who work on the move: drivers, delivery workers, engineers at job sites — using navigation, music, and video throughout their shift.
• Livestreamers, online sellers, content creators — uploading video is a heavy data activity.
• People in their first 3–6 months in Japan who don't want to sign a 2-year fixed-line contract yet but still need strong internet at home.

On the other hand, according to general Japanese telecom industry statistics, the average data usage per mobile subscriber in Japan is only around a few dozen GB per month. This means most ordinary users don't come close to 300GB. Don't choose based on the feeling that "more is always safer" — choose based on the number you've actually measured yourself.

Documents you'll need

For data-only SIM/eSIM plans (without a calling number), the procedure is usually simple. For voice-calling SIMs, requirements are stricter under Japanese regulations.

If you're using an eSIM, you'll also need to check two technical requirements: your device supports eSIM and your device is not SIM-locked. Phones bought in Vietnam as international versions usually work fine; used phones bought secondhand from a Japanese carrier are sometimes still locked. See detailed requirements for each plan on the products page.

Cost

Data plan prices change depending on timing and promotions, so please check the exact price at Monthly data SIM, Monthly eSIM, or Pocket WiFi. Below is how to compare costs correctly, instead of just looking at the first month's price:

• Calculate yen/GB based on actual usage, not the advertised yen/GB. If you buy 300GB but only use 60GB, your real unit price is 5 times higher than the advertised figure.
• Include upfront fees. Many plans have an activation fee (契約事務手数料), SIM fee, and shipping fee. Prepaid annual plans, such as 12-month prepaid SIM, are usually cheaper on a monthly basis but require a lump-sum payment.
• Compare with fixed-line internet. Fiber optic internet in Japan typically costs about 4,000–6,000 yen/month, plus installation fees and contract commitments, not to mention waiting for a technician to visit your home (which can take several weeks). If you're staying under 1 year or move often, a large data SIM usually has a lower total cost.
• Don't forget the hidden cost of running out of data: when your allowance runs out mid-month, speeds drop drastically, forcing you to buy additional data — and add-on data is always more expensive per GB.

For payment methods (bank transfer, card, convenience store, etc.), see the guide on the support page.

Timeline / processing time

• eSIM: usually the fastest — after your registration and payment are confirmed, a QR code is sent via email, and you can scan it to activate, typically the same day or within 1 business day.
• Physical SIM: sent via Japan Post, usually 1–3 business days depending on the area; remote areas or long holidays may take longer.
• Pocket WiFi: similar to physical SIM since the device must be shipped.
• Data cycle: data is allocated on a monthly cycle and usually does not roll over to the next month. Unused data is lost — another reason not to overbuy.
• When data runs out: most plans don't cut off the connection entirely, but instead reduce speed to a very slow rate until the next cycle begins.

Be sure to confirm the start date of your plan's cycle (activation date or the 1st of each month), since the usage stats on your device are calculated based on the cycle you set yourself, which may not match your carrier's actual cycle.

Where to register / where to go

• Register online: choose a plan on HD TELECOM's products page, fill in your information, and upload photos of your documents. Voice-calling SIMs have a separate form at the voice SIM registration page.
• In person at the office: HD TELECOM has an office in Shin-Okubo, Tokyo — visit if you'd like consultation in Vietnamese, want to check whether your phone supports eSIM, or need on-site setup.
• Support before and after purchase: see the support page for how to get in touch, payment methods, and setup instructions.

Common mistakes

• Buying based on a "just to be safe" feeling. This is the most common mistake. Many people buy the largest plan and then end up with over half their data unused every month.
• Measuring usage during an atypical week. Measuring during a long holiday week, a sick week spent watching movies at home, or a travel week will give you a figure that's way off from your normal routine.
• Forgetting that tethering consumes data extremely fast. When a laptop connects via a phone's hotspot, Windows/macOS may automatically download several GB of updates, and OneDrive/Google Drive may auto-sync. Turn on "metered connection" mode on your laptop.
• Letting videos autoplay at the highest quality. Watching 4K on a phone screen looks almost identical to 1080p to the naked eye, but uses 2–3 times more data. Go into your YouTube/Netflix/TikTok settings and limit quality when on mobile data.
• Confusing "out of data" with "network broken". Your phone still shows signal, you can still access LINE in text form, but videos won't play — this is usually a sign you've run out of data and been throttled.
• Not setting a data usage alert. Android lets you set an alert and a limit at your chosen GB level; on iPhone, you should check manually midway through the month.
• Choosing a data-only plan when you actually need a phone number. Many procedures in Japan (opening a bank account, registering a rental, submitting job applications) require a phone number that can receive calls. If so, consider a voice-calling SIM.
• Ignoring coverage and peak hours. A large data allowance doesn't mean it's always fast. In densely populated areas during lunch (12–1pm) and evening (7–10pm) peak hours, speeds may be slower than usual.

Frequently asked questions

Is 300GB a month a lot or a little?

It's a lot compared to the average user in Japan. 300GB is roughly equivalent to about 10GB/day, which is about 3–4 hours of 1080p video streaming per day, or enough to fully replace WiFi for a household of 1–2 people.

Where do I check how many GB I've used?

iPhone: Settings → Cellular → the stats section at the bottom of the page. Android: Settings → Network & Internet → Data usage. Remember to reset the stats at the start of your cycle so the number accurately reflects a single month.

Does unused data roll over to the next month?

Usually not. Most monthly plans reset your data allowance each cycle. You should confirm the specific terms of the plan you intend to buy before registering.

What happens if I run out of data mid-month?

Typically the connection isn't cut off entirely, but speed is reduced to a very slow rate — you can still send text messages, but video is nearly unwatchable. You can buy additional data or wait until the next cycle begins.

Is it okay to use a 300GB data SIM instead of home WiFi?

It's fine for 1–2 people, for online classes, Zoom meetings, and watching movies. If 4–5 people are using it simultaneously, or you need a stable connection for important work, you should use a pocket WiFi or fixed-line internet instead, since a phone acting as a constant hotspot will overheat and drain its battery quickly.

Does a data plan come with a Japanese phone number for calls?

No. A data plan only provides internet access. You can still make calls via LINE, Zalo, Messenger, and WhatsApp, but you won't be able to receive calls from a regular phone number. If you need a number, check out our voice-calling SIM.

Should I choose a physical SIM or an eSIM?

If your phone supports eSIM, it's more convenient since it's delivered via email, there's no waiting for the post, and you can't lose it. A physical SIM is better suited for older phones or people who want the flexibility to easily move it to another device.

I measured my usage at 120GB/month — which plan should I buy?

Add a 20–30% buffer to get about 145–160GB, then choose the closest plan tier above that number. Only jump up to 300GB if you're about to change your habits (for example, moving to a place without WiFi, or starting online classes).

References

• Apple Support — guide on viewing and resetting cellular data statistics on iPhone (support.apple.com).
• Google — Android Help: checking, setting alerts and limits for data usage (support.google.com).
• YouTube Help — video quality settings and data consumption (support.google.com/youtube).
• Netflix Help Center — controlling data usage based on streaming quality (help.netflix.com).
• Ministry of Internal Affairs and Communications of Japan (総務省) — mobile data traffic statistics in Japan, published periodically (soumu.go.jp).

The GB conversion figures in this article are average reference values; actual usage varies depending on the app, device, and signal quality. Terms regarding data allowance, post-data-cap speeds, and pricing vary by plan — please read the specific terms of the plan you purchase carefully.

Source verification date

The content and sources above were last verified on June 15, 2025. Carrier pricing and data policies may change, so please check the latest information on the product page before registering.

Need help choosing a plan?

If you've already measured your usage and know your GB number, you can view and compare options directly: Monthly data SIM, Monthly eSIM, 12-month prepaid data SIM, or Pocket WiFi.

And if you're not sure how much you use, just message HD TELECOM with a screenshot of your device's data usage stats — our Vietnamese-speaking support team will help estimate and recommend a plan that's just right, so you don't have to overbuy. Contact information and payment instructions are on the support page. You're also welcome to visit our office in Shin-Okubo, Tokyo, for an on-site device check and setup. More helpful articles are available on our blog.