There are many different log calculation formulae around the world, and one of most widely used is JAS (Japanese Agricultural Standard). This formula is being currently adopted in Japan, Chile, Eastern Asia and Oceania.
The JAS was developed in Japan for Roundwood measurement in the late 1940s and uses the narrow end of the diameter for volume calculation.
When using the method, some details are important to note: diameters (either smaller or larger than 14cm); rounding rules and log length.
For logs, less than 14 cm (nominally) on the small-end measurement needs to be taken through the narrow axis.
For logs with 14 cm and larger, two measurements need to be taken, through the narrow axis and the wide axis of the log end.
JAS rounds each log volume to 3 decimal places. There are two rounding options according to the final diameter result:
- Logs with less than 14 cm of diameter – the result will be rounded down.
- Logs with more than 14 cm of diameter – the result will be rounded down to the nearest even integer.
For logs less than 6m long:
V(m3) = (D²*L)/10000
where:
D – small-end diameter(cm), for less than 14 cm, the diameter is rounded down and after 14cm the diameter is rounded down to the nearest even integer.
L – Length(m)
For logs equal to or greater than 6m:
V(m3) = (D + [L’-4]/2)^2*(L/10000)
D – small-end diameter(cm), for less than 14 cm, the diameter is rounded down and after 14cm the diameter is rounded down to the nearest even integer.
L – Length(m)
L’ – length in meters rounded down to nearest whole number
Timbeter uses the exact average diameter as an input. As the rounding rules of JAS require rounding down, then our experience demonstrates that the results are very accurate and correct.
Timbeter displays on the screen the exact diameter with one decimal place (25,9 cm), but on the tally sheet, the number is rounded down according to the requirements (24 cm). So whenever there be a question what is the exact diameter of the log, it is easy to check.
Do you have any questions regarding JAS or any other formulas?
Did you know Timbeter has the JAS formula built into the software? Give Timbeter a trial with JAS today!
