---
title: "JAS Log Scaling: The Japanese Agricultural Standard Explained"
description: "How JAS scales round logs: the 1 cm / 2 cm diameter rounding rule, V = D² × L ÷ 10,000, the long-log adjustment, the oval-log rule, and why Asia-Pacific plantation trade quotes JAS cubic metres."
image: "https://nestingcalc.com/og-default.png"
url: "https://nestingcalc.com/guides/jas-log-grading-standard/"
locale: "en"
---

# JAS Log Scaling: The Japanese Agricultural Standard Explained

How JAS scales round logs: the 1 cm / 2 cm diameter rounding rule, V = D² × L ÷ 10,000, the long-log adjustment, the oval-log rule, and why Asia-Pacific plantation trade quotes JAS cubic metres.

## The volume formula

JAS measures the small-end diameter under bark and rounds it **down**: below 14 cm to the nearest 1 cm, at 14 cm and above to the nearest even 2 cm step — 25.9 cm scales to 24. For logs up to 6 m, volume is **V = D² × L ÷ 10,000** (D in cm, L in m), rounded to 3 decimals. A 24 cm × 4 m log therefore scales 576 × 4 ÷ 10,000 = **0.230 m³**.

## Logs longer than six metres

Longer logs add a taper allowance to the diameter: **D\_eff = D + (⌊L⌋ − 4) ÷ 2** centimetres, then the same formula. A 24 cm log 8 m long gets D\_eff = 24 + (8 − 4)/2 = 26 → 26² × 8 ÷ 10,000 = **0.541 m³**. The add-on approximates the taper a small-end measurement otherwise misses.

## Oval logs

When a log is oval, both axes are scaled separately and averaged. On top of that, an ovality correction may apply: with a short axis of 14–40 cm and a long-short difference of 6 cm or more, add 2 cm per full 6 cm of difference; above 40 cm short axis, 2 cm per 8 cm. Example: axes 22 and 30 scale to 22 and 30, average 26, difference 8 ≥ 6 → +2 → D = 28; at 5 m: 784 × 5 ÷ 10,000 = **0.392 m³**.

## Why D² (and no π/4)

True cylinder volume would be π/4 × D² × L, so a bare D² × L reads ≈ 27% (4/π) higher than a cylinder of the same D. That is deliberate: D is a small-end diameter rounded down, and the missing π/4 approximates the taper between the small end and the rest of the log. For typical plantation logs the two effects largely cancel — which is why JAS cubic metres track commercial reality closely enough to price shipments on.

## Grading beyond volume

JAS also standardises quality: rules for knots, sweep, splits and ovality, with defect deductions agreed contract by contract. Vietnam, Japan and much of the Asia-Pacific plantation trade quote roundwood in JAS m³ precisely because the scale is unambiguous — but mixing scales inside one deal (JAS for intake, Hoppus for stock, true m³ for export) is where margin leaks; pick one and reconcile the rest with conversion ([Hoppus Formula Explained: Quarter-Girth Log Measurement](https://nestingcalc.com/guides/hoppus-formula-explained/) for Hoppus).

## Scale a load in seconds

[JAS log scale](https://nestingcalc.com/jas-log-scale-calculator/) implements the exact rounding, ovality and long-log rules above — including the per-axis averaging — and multiplies by piece count for a truck or container load. For true-volume scaling by mid-diameter, [Log volume (Huber/Smalian)](https://nestingcalc.com/log-volume-calculator/) applies Huber, Smalian and Newton; comparing the two on the same log is the fastest way to understand your own taper bias.

[JAS log scale](https://nestingcalc.com/jas-log-scale-calculator/) [Open the linear cutting calculator](https://nestingcalc.com/linear-cutting-calculator/)

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