Mailing a letter within Japan is straightforward once you know three things: the sealed envelope’s dimensions, its total weight, and whether you need an optional service such as express or tracking.

The short version is: address and seal the envelope, measure it, calculate the postage, attach enough stamps, and place it in a mailbox. Use a post-office counter if you are unsure about the rate or want a service that needs acceptance at the counter.

1. Write the destination and return address

Copy the recipient’s address exactly as they gave it to you, including the seven-digit postal code. A Japanese postal code is normally written as three digits, a hyphen, and four digits, for example 100-0001.

If you write the address horizontally, put the recipient’s details in the center of the front and your return address in a smaller block on the back. Keep stamps together at the upper-right corner of a horizontally addressed envelope.

Apartment and office addresses should include the building name and room or floor number. Do not translate a Japanese building name unless the recipient provided an English version.

2. Choose an envelope and seal it

Common envelope labels in Japanese stationery shops include:

  • 長形3号 (Nagagata 3): a narrow envelope for A4 paper folded in thirds.
  • 角形2号 (Kakugata 2): a larger envelope that holds A4 paper flat.
  • 角形A4号 (Kakugata A4): a close-fitting A4 envelope.

The envelope name alone does not determine the postage. Paper, folders, clips, and other contents all count toward the total weight, while thickness can move the item into another rate category.

Seal the envelope before weighing it. That gives you the number that matters at the post office.

3. Measure the sealed letter

For an ordinary standard-size letter (定形郵便物), the envelope must be 14–23.5 cm long, 9–12 cm wide, no more than 1 cm thick, and no more than 50 g. The current base postage is ¥110.

An envelope that is larger or thicker can still travel as non-standard mail (定形外郵便物), but it uses a different price table. A typical A4 envelope sent flat falls into this category.

Use the Japan Postage Calculator to enter the exact weight and thickness. If you do not have a scale, it can estimate weight from an envelope preset and the number of A4 sheets. Treat an estimate near a weight boundary cautiously: different paper and envelope stock can change the result.

4. Buy and attach the stamps

You need stamps whose combined value equals the calculated total. You can buy the exact postage at a post-office counter. If you already have stamps, several denominations can be used together.

Keep every stamp fully on the envelope and do not overlap them. If there is not enough room or you are unsure about the total, take the sealed item to the counter instead of guessing.

Useful Japanese at the counter:

この封筒を送りたいです。
Kono fūtō o okuritai desu.
“I’d like to mail this envelope.”

To ask for the ordinary service, say:

普通郵便でお願いします。
Futsū yūbin de onegaishimasu.
“Regular mail, please.”

5. Send it from a mailbox or counter

An ordinary stamped letter that fits through the slot can go into a red Japan Post mailbox. Check the slot labels because a mailbox may separate regular letters from larger items.

Use the post-office counter when:

  • the envelope is close to a size or weight limit;
  • you want express, tracking, or registered service;
  • the contents are valuable or difficult to replace;
  • you are not sure which mail category applies.

Tracking and registered services cost more than ordinary postage. Some services also require the clerk to record acceptance, so attaching extra stamps is not always the whole process.

Common mistakes to avoid

Pricing an open envelope

The final piece of tape, label, or extra document adds weight. Seal first and weigh second.

Assuming every A4 envelope has one price

A4 describes the paper, not the finished mail item. Folding the paper into a smaller envelope can produce a different category from sending it flat.

Sending cash as an ordinary letter

Cash must not be placed in ordinary domestic mail. Japan Post has a dedicated registered-cash service called 現金書留 (genkin kakitome) with its own envelope and procedure.

Using a calculated rate after prices change

Postal prices can change. This site records when its rate table was checked, and the official Japan Post domestic letter rate page remains the final authority.

Before you leave home

Use this quick checklist:

  1. Recipient address and postal code are complete.
  2. Return address is included.
  3. The envelope is sealed.
  4. Size, thickness, and total weight are known.
  5. Postage covers the base rate and any optional service.

If all five are true, an ordinary letter is ready for the mailbox. When one is uncertain, the post-office counter is the safest next stop.