そろばん入門
How to Use an Abacus (Soroban)
A beginner's guide to reading the Japanese soroban — the same abacus you can play with on the Abacus Alive home page.
Meet the beads
A soroban has vertical rods, and each rod stands for one place value: ones, tens, hundreds, and so on, reading right to left. A horizontal bar called the reckoning beam splits every rod into two zones.
- Heaven bead (above the beam): each rod has one, worth 5.
- Earth beads (below the beam): each rod has four, worth 1 each.
A bead only counts when it touches the beam. Slide the heaven bead down to add 5; slide earth beads up to add 1 each. Beads resting away from the beam are worth nothing.
Reading a number
Each rod shows one digit from 0 to 9: the heaven bead (5 if it's down) plus the earth beads that are pushed up (0–4). So a rod reads 7 when the heaven bead is down and two earth beads are up (5 + 2).
Read the rods from left to right and you have the full number — the rightmost rod is the ones place, the next is tens, then hundreds, and so on.
Try it yourself
Click the beads to move them, or pick a number below and watch the rods set it. The beads are showing 0 right now.
Adding and carrying
To add, push more beads toward the beam. When a rod runs out of beads, you use a complement: to add 4 when only 2 earth beads are free, bring down the heaven bead (add 5) and take away 1 — because 4 is "5 minus 1".
When the rod is completely full (already 9), you carry to the next rod: adding 1 to 9 means adding 1 on the rod to the left and clearing this one. These two moves — complements of 5 and carries of 10 — are the whole secret of soroban arithmetic.
The home page can explain every step for you: turn on Explain steps, do any calculation, and watch each carry and borrow described rod by rod.