囲碁将棋盤 榧寿堂 ／ Reading Japanese Go Board Dimensions: Shaku and Sun, Why the Board Is Longer Than It Is Wide, and What Older Records Show
Reading Japanese Go Board Dimensions: Shaku and Sun, Why the Board Is Longer Than It Is Wide, and What Older Records Show
If you look at go boards from Japanese makers or shops, the dimensions are often given in shaku (尺) and sun (寸), not centimetres. And if you measure a full-size board, you will find it is not square: it is a little longer in one direction.
This page explains how to read those numbers, why the board is shaped that way, and what a few older recorded boards measured.
The short answer
- 1 sun ≈ 3.03 cm, and 1 shaku = 10 sun ≈ 30.3 cm (the Nihon Ki-in gives 1 sun as about 3.03 cm).
- A full 19×19 board is commonly given as 1 shaku 5 sun long × 1 shaku 4 sun wide, about 45.5 × 42.4 cm.
- The longer side runs from player to player. The usual explanation is that the players look down at the board at an angle, so a slightly longer board looks closer to square from where they sit.
- Thickness is also stated in sun. Kuroki Goishiten (a stone and board maker) says pedestal boards are commonly 3 to 8 sun (about 9–24 cm) and table boards 2 sun (about 6 cm).
Converting shaku and sun
| Japanese | Sun | Centimetres (approx.) |
|---|---|---|
| 1 sun (一寸) | 1 | 3.03 cm |
| 2 sun | 2 | 6.1 cm |
| 3 sun | 3 | 9.1 cm |
| 5 sun | 5 | 15.2 cm |
| 6 sun | 6 | 18.2 cm |
| 1 shaku (一尺) | 10 | 30.3 cm |
| 1 shaku 4 sun | 14 | 42.4 cm |
| 1 shaku 5 sun | 15 | 45.5 cm |
Smaller units also appear in older records: 1 bu (分) = one tenth of a sun, about 3 mm. The Nihon Ki-in uses it for stone sizes, for example: a white stone of 21.9 mm (7 bu 2 rin) and a black stone of 22.2 mm (7 bu 3 rin).
Why the board is longer than it is wide
The standard full-size board is longer from player to player than from side to side. The explanation most often given (for example in the Japanese and English Wikipedia articles on go boards) is about viewing angle: each player looks down at the board from one end, so distances running away from them look shorter. Making the board slightly longer in that direction keeps the grid looking even.
This is the commonly stated reason, not a rule set by a governing body. What matters in practice is simple: place the board so its longer side points from you to your opponent. A shogi board is shaped the same way; see Shogi Board Sizes, and How They Differ From a Go Board.
How thickness is stated
For a pedestal board, Kuroki Goishiten says: “the thickness of a pedestal board is the thickness of the board body, not including the legs.” Common thicknesses, according to the same maker:
| Type | Common thickness |
|---|---|
| Pedestal board (脚付盤) | 3 to 8 sun (about 9–24 cm) |
| Table board (卓上盤) | 2 sun (about 6 cm) is common; table boards range from about 0.3 to 4 sun |
When you compare listings, keep board thickness and overall height including legs separate. A listing that says “6 sun” is describing the body only. Choosing a thickness is covered in Go & Shogi Board Thickness, and the legs and the recess underneath in Go Board Legs and the Chidamari.
Thick one-piece pedestal boards need very large trees. Kuroki Goishiten says a one-piece pedestal go or shogi board requires a tree of roughly 200 to 800 years old, which is why thick one-piece boards are scarce.
What older recorded boards measured
The Japanese Wikipedia article on go boards lists a few historical boards. Two examples, converted with 1 sun ≈ 3.03 cm:
| Record | Length | Width | Thickness |
|---|---|---|---|
| Standard board of Hon’inbō Dōetsu | 1 shaku 4 sun 5 bu (about 43.9 cm) | 1 shaku 3 sun 5 bu (about 40.9 cm) | 3 sun 9 bu (about 12 cm) |
| Present-day standard | 1 shaku 5 sun (about 45.5 cm) | 1 shaku 4 sun (about 42.4 cm) | varies |
These are individual records, not proof that every board of a period had the same size. They do show that the length has stayed in roughly the same 44–46 cm range, and that the board was already longer than it was wide.
Reading a Japanese listing
- Find the length and width (縦・横). For a 19×19 board they should be close to 45.5 × 42.4 cm.
- Find the thickness (厚み) in sun and convert it. Check whether it is the body only.
- For a pedestal board, check the overall height (高さ) separately if it matters for your room.
- If the board is a 9×9 or 13×13, the size is different; see 9×9, 13×13 or 19×19?.
If a measurement is unclear, ask the seller or maker before you buy. Choosing a board overall is covered in Choosing a Go Board.
FAQ
Is every full-size go board exactly 45.5 × 42.4 cm? That is the commonly given standard. Individual boards and makers can differ slightly, so check the listing.
Why do Japanese listings still use sun? It is the traditional unit for boards, and thicknesses such as “5 sun” or “6 sun” are how boards are commonly named. Convert with 1 sun ≈ 3.03 cm.
Does a thicker board mean a bigger playing surface? No. Thickness changes the height and weight of the board, not the length and width of the playing surface.
Sources (checked 18 October 2026): Nihon Ki-in — 囲碁雑学 (unit of sun, stone sizes) / Kuroki Goishiten — 碁盤の選び方 (thickness, tree age). The standard length and width, the viewing-angle explanation and the historical records follow the Japanese and English Wikipedia articles on go boards. Conversions use 1 sun ≈ 3.03 cm and are approximate.