Japan Post’s Mini-Letter (郵便書簡, yūbin shokan) costs ¥85 for a finished item weighing no more than 25 g and measuring no more than 1 cm thick. Check the folded letter sheet together with everything enclosed. If either limit is exceeded, Japan Post says nonstandard letter postage applies—not simply the ordinary ¥110 standard-letter rate. Mini-Letter description and limits · Japan Post’s enclosure FAQ
Start with the correct stationery
A Mini-Letter is Japan Post’s combined letter sheet and envelope, with a printed postage mark. It is not any small envelope with an ¥85 stamp attached. Its low weight limit makes the packaging decision part of the postage decision. Japan Post: Mini-Letter
Before writing and sealing it, put the sheet, enclosure and any intended protection together on a scale. Check the thickness of the completed arrangement too. An enclosure can be light enough but too thick; a flat enclosure can be thin enough but too heavy.
This is a preparation procedure, not a tested packaging method. Do not reduce necessary protection simply to make a number fit.
The old “paper and photographs only” description is outdated
Japan Post announced that, from October 1, 2024, it would remove the Mini-Letter restriction that limited enclosures to thin items such as photographs and pieces of paper. It introduced a 1 cm thickness limit while retaining the 25 g weight condition. The current FAQ confirms the thickness and weight limits. Japan Post’s dated change notice · Current enclosure FAQ
That change does not mean every object is suitable for this stationery. The notice concerns a specific enclosure restriction; it does not grant a blanket exception from other postal rules or establish that a delicate object will survive mailing. For an unusual item, describe it accurately at the counter before choosing the packaging.
Compare the completed item, not just its contents
The following are hypothetical examples. They are not measurements of Japan Post stationery or actual mailed items.
| Completed item | Weight/thickness decision |
|---|---|
| 23 g and 0.8 cm thick | Within both Mini-Letter limits |
| 26 g and 0.8 cm thick | Too heavy for the ¥85 Mini-Letter rate |
| 23 g and 1.2 cm thick | Too thick for the ¥85 Mini-Letter rate |
Suppose an enclosure weighs 20 g and everything else adds 4 g. The combined weight is 24 g. If an additional protective piece adds 2 g, the new total is 26 g. That small addition crosses the limit even though the enclosure itself is unchanged.
These calculations deliberately use assumed weights. There is no universal allowance for “one photograph” or “one protective sleeve”; weigh the actual combination. If the reading sits on the boundary and your scale is imprecise, have the counter check it.
Repacking can change the category
Japan Post specifically recommends considering a standard-size envelope when a Mini-Letter exceeds its limit. A Mini-Letter over 25 g does not automatically acquire the classification of a standard-size envelope. Japan Post: exceeding Mini-Letter limits
For a hypothetical 26 g item that remains within the nonstandard specified-size limits, the listed base postage is ¥140. Compared with an ¥85 postage mark, that is a ¥55 difference. Alternatively, repacking into an ordinary envelope that meets all standard-letter conditions, including a final weight within 50 g, would put the base postage at ¥110. That comparison excludes the new envelope’s cost and any optional service. Japan Post’s domestic rate table
Repacking does not automatically guarantee eligibility: the new envelope and protection change the measurements. Measure again, then choose the rate. If the Mini-Letter is already prepared, take it to the counter before adding stamps based only on the weight.
This guide covers domestic Mini-Letters in Japan. It is desk research, not a hands-on mailing test. Rates and rules were checked on October 12, 2026; the examples do not establish that a particular item will be accepted for mailing.