Nagasa Converter — Shaku, Sun & Bu to Centimetres
Convert traditional Japanese blade-length units (shaku · sun · bu) to centimetres and inches — and back — with automatic legal classification as tantō, wakizashi or katana.
Japanese blade length (nagasa) is traditionally recorded in shaku, sun and bu — the units you will find in sword books, NBTHK papers and auction descriptions. One shaku is exactly 10/33 of a metre (30.30 cm). Convert in either direction below; the tool also tells you whether the length legally classifies the blade as a tantō, wakizashi or katana.
Shaku · sun · bu → centimetres
Or the reverse
Centimetres / inches → shaku · sun · bu
Nagasa is measured in a straight line from the mune-machi (back notch) to the tip of the kissaki — not along the curve of the blade.
The units
| Unit | Kanji | Value | Metric |
|---|---|---|---|
| Shaku | 尺 | 10/33 metre | 30.303 cm (11.93 in) |
| Sun | 寸 | 1/10 shaku | 3.030 cm (1.19 in) |
| Bu | 分 | 1/10 sun | 3.03 mm (0.12 in) |
A typical katana nagasa of 2 shaku 3 sun 5 bu therefore equals 71.2 cm. You will see this written in Japanese as 二尺三寸五分.
Legal classification by nagasa
Under the Japanese registration system (tōrokushō), blade category is determined purely by nagasa:
| Classification | Nagasa | Metric |
|---|---|---|
| Tantō 短刀 | under 1 shaku | < 30.3 cm |
| Wakizashi 脇差 | 1 to 2 shaku | 30.3 – 60.6 cm |
| Katana / tachi 刀・太刀 | 2 shaku and above | ≥ 60.6 cm |
These thresholds matter for registration and export paperwork: a blade of 59.8 cm is legally a wakizashi even if it looks like a short katana. Read more about Japanese sword registration in our tōrokushō guide, or browse our antique katana and wakizashi — every listing shows the exact nagasa.
Frequently asked questions
How long is a shaku in cm?
One shaku (尺) is exactly 10/33 of a metre — 30.303 cm, or about 11.93 inches. It divides into 10 sun (寸, 3.03 cm each), and each sun into 10 bu (分, 3.03 mm each).
How is nagasa measured?
Nagasa is the straight-line distance from the mune-machi (the notch at the back of the blade where the tang begins) to the very tip of the kissaki. It ignores the curvature (sori) and excludes the tang (nakago), so the overall sword is always longer than its nagasa.
What length makes a blade a katana rather than a wakizashi?
Two shaku — 60.6 cm. Blades of 2 shaku or more are classified as katana (or tachi), between 1 and 2 shaku as wakizashi, and under 1 shaku (30.3 cm) as tantō. This is the legal definition used on Japanese registration papers.
Why do Japanese sword papers not use centimetres?
Tradition. The shaku-sun-bu system predates the metric system by over a thousand years, and the sword world kept it. Modern tōrokushō registration cards actually record nagasa in centimetres, but books, dealers and NBTHK descriptions still quote shaku and sun.