How to use
Type the **7-digit postal code** (`150-0043` or `1500043` — dash optional). The tool calls zipcloud (the Japan Post postal-data API) and **auto-fills prefecture, city / ward, and town** in kanji for display, using the katakana reading to generate the English romanization. The lookup fires automatically the moment you finish typing the 7th digit; Enter or the "Look up address" button also triggers it.
Then enter the parts the postal code can't tell you: **block-lot-number** (`6-52-3`), optional **apartment / building name**, and optional **room number** (`A-305`). These three fields cannot accept kanji because kanji → reading conversion needs a morphological dictionary (kuromoji, ~10 MB) that would bloat the page — type the kana reading or romaji form instead. Building names can be in kana (`こーぽほしがおか` → `Kopo Hoshigaoka`) or directly in romaji (`Sky Hills` — passed through).
Two outputs render side-by-side, each with its own copy button:
- **Envelope format** — three lines ready to paste on an airmail label.
- **Form fields** — Address Line / City / State or Region / Country / ZIP, ready to fill in an online form.
Convention choices the tool makes:
- **Prefecture suffix retained**: `Tokyo-to`, `Kyoto-fu`, `Aichi-ken`, `Hokkaido` — matching the convention seen on Japanese English-address forms. For international shipping you can drop `-to` / `-fu` / `-ken` if your carrier prefers; both forms route correctly through Japan Post.
- **Composite cities split correctly**: 横浜市青葉区 → `Yokohama-shi Aoba-ku`, 札幌市中央区 → `Sapporo-shi Chuo-ku`.
- **Long vowels dropped by default** (`Tokyo`, not `Tōkyō` or `Tookyou`) per Japan Post and passport conventions; uncheck the option to preserve the doubled-vowel form.
- **"Japan" always appended** to the envelope output and the Country field. International mail requires it; for domestic Japanese mail or forms with a separate country field, ignore that line.
Examples
Tokyo apartment for international shipping
Input
postal: 150-0043 (auto-fills 東京都 / 渋谷区 / 道玄坂)
banchi: 2-1-1
building: まるやまビル
room: 301
Output
— Envelope —
301 Maruyamabiru, 2-1-1 Dogenzaka,
Shibuya-ku, Tokyo-to 150-0043
Japan
— Form fields —
Address Line: 301 Maruyamabiru, 2-1-1 Dogenzaka
City: Shibuya-ku
State / Province / Region: Tokyo-to
Country: Japan
ZIP / Postal code: 150-0043
Typical foreign-resident apartment in Shibuya. Three points worth flagging: (1) the tool concatenates kana runs into a single word (`まるやまビル` → `Maruyamabiru`) — for clearer word boundaries, type the building with a space (`まるやま ビル`) or directly in romaji (`Maruyama Biru`); (2) `Biru` (ビル) is *not* translated to "Building" because Japanese local couriers expect to see the romanized Japanese word as a visual cue; (3) the Address Line field condenses room + building + banchi onto one line because most online forms expose only one Address Line input — split it across multiple lines yourself if your carrier offers Address Line 2.
Composite city — Yokohama 政令指定都市
Input
postal: 225-0011 (auto-fills 神奈川県 / 横浜市青葉区 / あざみ野)
banchi: 1-5
building: (empty)
room: (empty)
Output
— Envelope —
1-5 Azamino,
Yokohama-shi Aoba-ku, Kanagawa-ken 225-0011
Japan
— Form fields —
Address Line: 1-5 Azamino
City: Yokohama-shi Aoba-ku
State / Province / Region: Kanagawa-ken
Country: Japan
ZIP / Postal code: 225-0011
横浜市青葉区 is a **composite city / ward** — Yokohama is one of Japan's 20 designated cities (政令指定都市) that contain wards (区), structurally similar to how New York contains boroughs. The tool detects the composite structure from the kanji (two suffix characters 市 and 区) and splits the katakana reading (ヨコハマシアオバク) accordingly, producing two segments — `Yokohama-shi Aoba-ku`. Other designated-city addresses follow the same pattern: 大阪市浪速区 → `Osaka-shi Naniwa-ku`, 名古屋市中区 → `Nagoya-shi Naka-ku`, 福岡市博多区 → `Fukuoka-shi Hakata-ku`. The Address Line is short in this example because building and room are empty — only the banchi-number plus town appear.
Long-vowel handling — Osaka Dotonbori
Input
postal: 542-0071 (auto-fills 大阪府 / 大阪市中央区 / 道頓堀)
banchi: 1-2
Kana readings: オオサカフ / オオサカシチュウオウク / ドウトンボリ
Output
— Drop long vowels ON (default) —
1-2 Dotonbori, Osaka-shi Chuo-ku, Osaka-fu 542-0071, Japan
— Drop long vowels OFF —
1-2 Doutonbori, Oosaka-shi Chuuou-ku, Osaka-fu 542-0071, Japan
道頓堀 reads ドウトンボリ — with the default drop, `dou` → `do` and the result becomes `Dotonbori`; uncheck the option to keep `Doutonbori`. The city 大阪市中央区 contains two long-vowel sequences (オオサカ → Osaka / Oosaka, チュウオウ → Chuo / Chuuou), both collapse under drop. Prefecture names are looked up from a hardcoded 47-entry table for accuracy, so `Osaka-fu` does not shift with the toggle — this is intentional because the canonical English forms of all 47 prefectures are well-known and stable, and we don't want a toggle to ever produce `Oosaka-fu` (which no Japanese postal label uses). The drop-on form (`Tokyo`, `Osaka`, `Kyoto`) is what foreign government forms, banks, and shipping carriers expect; drop-off (`Tookyou`, `Oosaka`, `Kyouto`) is sometimes seen in academic linguistic transliteration or in children's textbooks where each kana is shown explicitly.
FAQ
What is Hepburn romanization and how does it differ from Kunrei?
**Hepburn** (ヘボン式) was created by American missionary James Curtis Hepburn in 1867 to romanize Japanese for English-speaking readers, prioritizing what looks natural to English eyes. Examples: し → `shi`, ち → `chi`, つ → `tsu`, ふ → `fu`, じ → `ji`. **Kunrei-shiki** (訓令式) is the 1937 official Japanese government standard, designed by Japanese linguists for internal consistency: し → `si`, ち → `ti`, つ → `tu`, ふ → `hu`, じ → `zi`. Hepburn is what foreigners use almost universally — passports, road signs, station signs, business cards, this tool. Kunrei lives on in Japanese elementary-school education and some academic linguistics but rarely appears in English-language contexts. A modern variant, **Nihon-shiki**, predates both and is similar to Kunrei but stricter; it is the basis for ISO 3602. For postal addresses, always use Hepburn.
Do I need "Japan" at the end? The tool always appends it.
**For international mail**: yes, always — the destination country must appear in English on the bottom line. Without `JAPAN` (or `NIPPON`), international postal sorting won't route the letter to Japan Post. **The tool always appends `Japan`** in both the envelope and the Country field; you can drop it manually if you're posting from within Japan or if an online form has a separate Country dropdown. **For visa / employer / bank forms**: most ask for the country in a separate field — do not duplicate it on the Address Line. **Capitalization**: international convention is ALL CAPS (`JAPAN`); Japan Post accepts mixed case. The tool outputs `Japan` (title case) — upper-case it manually if your carrier requires.
Why can't I type kanji in the building / room fields?
**Prefecture, city / ward, and town are no longer typed by hand** — they're filled automatically from the postal-code lookup, which returns both the kanji form (for display) and the katakana reading (for romanization). You don't need to know the reading of any place name; the lookup handles it.
The **block-lot-number**, **apartment / building name**, and **room number** fields, however, still cannot accept kanji. Postal-code lookup doesn't cover them — they're user-typed — and converting arbitrary kanji input to its romaji reading requires a morphological dictionary like kuromoji (~10 MB minified), too heavy for a static utility page.
In practice this rarely bites: block numbers like `6-52-3` and room numbers like `A-305` don't involve kanji, and most apartment names are written in katakana (`コーポ星ヶ丘`, `セジュール`) or English (`Sky Hills`, `Mori Tower`) already. If you have a kanji-only building name like `森ビル`, look up the reading on the building's website or Google Maps, then type it as kana (`もりビル`) or romaji (`Mori Biru`).
Why does the tool keep `-to` / `-fu` / `-ken` instead of dropping them?
Japan has 47 first-level administrative divisions called 都道府県 (todōfuken), grouped into four categories: **1 都** (Tokyo), **1 道** (Hokkaido), **2 府** (Kyoto, Osaka), and **43 県** (everyone else). Administratively the four are nearly identical today; the labels are vestigial from Meiji-era reorganization.
For English romanization, two conventions coexist:
- **Drop the suffix** (`Tokyo`, `Kyoto`, `Aichi`) — used by Japan Post for international mail, by passports, by most foreign references. Hokkaido is the only exception because `Hokkai` would be awkward.
- **Keep the suffix** (`Tokyo-to`, `Kyoto-fu`, `Aichi-ken`, `Hokkaido`) — used on many Japanese domestic English forms (online shopping, banking, business registration where the legal English form may include the suffix).
**This tool follows the second convention** — keeping the suffix — to match the format users see when filling out Japanese-issued English forms. For international shipping you can manually delete the `-to` / `-fu` / `-ken` from the State field; both forms route correctly through Japan Post and international carriers. Hokkaido stays as `Hokkaido` either way.
How does the postal-code lookup work? Is the data reliable?
The tool calls **zipcloud** (`zipcloud.ibsnet.co.jp`), a free public API maintained by IB Shinano that mirrors Japan Post's official postal-code dataset (KEN_ALL.CSV). Japan Post publishes updated postal data on the last business day of every month; zipcloud refreshes shortly after. The API has been stable since 2013, requires no authentication, and is CORS-enabled — calls go directly from your browser to zipcloud, never through our server.
**Reliability**: very high for established addresses. The dataset is the same one Japan Post uses internally for sorting, so a postal code that the API returns will be correctly recognized by all domestic and international carriers. Edge cases: newly-issued postal codes (typically corporate buildings or new developments) may take 1–2 months to appear after assignment; a small fraction of historical addresses have unusual kana that don't romanize cleanly. For mission-critical use (legal documents, visa applications), cross-check with Japan Post's own English postal lookup at `post.japanpost.jp`.
**What if zipcloud goes down?** The tool will show a "lookup failed" error. As a static client-side tool we have no fallback dataset bundled (~12 MB CSV would be too heavy). In that case, find the kana reading on Google Maps or Wikipedia, then type the address structure manually into another tool that accepts manual fields.
What does the 7-digit postal code mean? Is the dash mandatory?
Japanese postal codes have **7 digits**, conventionally written `NNN-NNNN`. The first 3 digits identify the prefecture and a broad delivery district; the last 4 identify a smaller area, sometimes a single building for large business addresses.
The dash is **not required** — both `1500043` and `150-0043` resolve identically. The tool strips non-digits before lookup, so any formatting works. Lookup fires automatically as soon as you finish typing the 7th digit; you can also press Enter or click "Look up address".
International forms sometimes have a 5-character "postal code" limit because that matches US ZIP codes (`12345`); Japanese 7-digit codes may need to be split across two fields, or you can omit the dash to fit one. The system was introduced in 1968 with 5 digits and expanded to 7 in 1998 — older archived addresses may still show 5-digit codes (`150-43` for Shibuya), which route correctly via Japan Post but won't resolve in this tool's lookup.
What about Hong Kong / Singapore / Korea — same address logic?
No — each East Asian country has its own conventions. **South Korea** ran a major address reform in 2014, switching from a parcel-numbered system (지번 주소) to a street-name-numbered system (도로명 주소) closer to Western practice. New Korean addresses already look Western-ordered without conversion: "123 Sejong-daero, Jongno-gu, Seoul 03172". For older parcel-format Korean addresses, our **`address-en-kr`** sister tool handles the conversion. **Singapore** uses an English address natively (one of its official languages) — no romanization needed; just write the address. **Hong Kong** uses English in addresses for international mail; local mail uses Chinese. **Taiwan** addresses follow a structure closer to Japan (large-to-small in Chinese, small-to-large in English) but use Pinyin or Wade-Giles romanization rather than Hepburn. **Mainland China** uses Pinyin romanization for addresses but English-language address structure is identical to Western order; the conversion is mostly mechanical street-name romanization.
Related concepts
Japanese addressing reflects centuries of organic urban growth rather than rational street planning. The **chome-banchi-go (丁目–番地–号) system** identifies a chome (district within a town), a banchi (block within the chome, numbered sequentially as buildings were constructed historically, not geometrically), and a go (the specific building or lot within the block). The numbering follows **chronological construction order in many areas**, so banchi 1, 2, and 3 within the same chome may not be adjacent — they were just the first, second, and third lots subdivided. This is why Japanese taxi drivers historically used landmark-based navigation rather than street addresses, and why the universal **post-1962 koban (police box) directory system** existed: officers in every neighborhood knew the local building numbering by heart and could point lost visitors toward the right block. The 1968 introduction of the **Japan Post 7-digit code** (then 5 digits, expanded to 7 in 1998) and modern GPS apps reduced reliance on koban directions, but Japanese GPS still occasionally directs users to the wrong building because banchi-numbering is unpredictable.
The **romanization layer** sits on top of an already-complex addressing system. Hepburn is the dominant standard for foreign-facing romanization, but several variants exist that vary the long-vowel treatment, the apostrophe in cases like `n'g`, and the conversion of voiceless h-row vowels. **Modified Hepburn** (used by Library of Congress, Wikipedia) adds macrons over long vowels; **Revised Hepburn** (used by Japan Post, passports) drops them; **Traditional Hepburn** uses double letters. Within Japan, official body signage at major stations (Tokyo, Osaka, Kyoto) has migrated from Traditional Hepburn (1950s) to Modified Hepburn (2000s) and now uses Modified Hepburn nearly universally. Foreigner-facing documents — passports, residence cards, driver's licenses — still use Revised Hepburn (no macrons) because most foreign keyboards cannot type macrons easily. This tool follows the Revised Hepburn / Japan Post convention by default (drop long vowels) with an option to switch to the doubled-vowel form.
Three adjacent **identity systems** intersect with Japanese addresses. The **My Number (マイナンバー)** national ID system introduced in 2015 includes address as a core attribute; address changes require formal notification to city hall, which propagates through tax, pension, health insurance, and bank records — a much tighter coupling than US Social Security. The **gaikokujin tōroku (foreign-resident registration)** and **zairyū card (residence card)** systems require non-citizens to carry physical proof of their registered address; police checks routinely include address verification. Finally, **business registration** in Japan ties extensively to the legal address (本店所在地, "head office location") — moving a company's registered address is a formal process triggering tax-jurisdiction changes and corporate-registry updates. For an outside reader, these systems make a Japanese postal address feel more like a US driver's license — a load-bearing legal identifier rather than a delivery instruction.
