JAS Log Scale Calculator (Japanese Agricultural Standard)
Scale logs to the JAS rule with diameter rounding and ovality — free.
Enter the short-axis diameter and length; the JAS calculator applies the official rounding (floor to 1 cm below 14 cm, to even 2 cm above), handles oval logs and lengths over 6 m, and totals a load with quantity.
FAQ
How does JAS round the diameter?
Below 14 cm the diameter is floored to whole centimetres; at 14 cm and above it is floored to the next even 2 cm — for example 25.9 cm scales to 24 cm. Volume is D² × L ÷ 10 000, rounded to 3 decimals.
What changes for logs longer than 6 m?
A length allowance is added to the scaled diameter: D_used = D + (floor(L) − 4) ÷ 2 in cm. A 30 cm log of 7.6 m is scaled with 31.5 cm and gives 0.754 m³.
How are oval logs scaled?
Measure both axes, scale each with the rounding rule and average them. For a short axis of 14–40 cm add 2 cm for every 6 cm difference between the axes (2 cm per 8 cm above 40 cm) — enable the adjustment above.