I am new to sawmilling and I would appreciate it if you could give me a formula for calculating board feet of usable boards from a specific size log, i.e. 18" x 10'. I understand that this might be different if sawn differently -- quartered or whatever.
There are probably over 100 log rules that estimate footage in logs. Most of them are empirical. However, a few are formula-based. Some have regression equations. For example, Scribner is V = (0.0494 x Dia x Dia x Length) - (0.124 x Dia x Length) - (0.269 x Length).
International is V = 0.905 x ([0.22 x Dia x Dia] - [0.71 x Dia]) for every four-foot length of log. There is also a longer equation for any length log.
Doyle is V = [L x (Dia - 4) x (Dia - 4)] / 16
Doyle is also V = [0.0625 x Dia x Dia x Length] - [0.500 x Dia x Length] + [1.000 x length]
In all cases, diameter is inside bark, small end. It is rounded to the closest inch. (Sometimes the scale includes the outside bark diameter.)
Length is the last full foot, no fractions.
Often the footage is rounded to the closest 10 BF. Then, since all the numbers are a multiple of 10, the "0" is dropped (e.g., 120 BF becomes 12) and the scale is called "decimal" which means you have to multiply by 10. But sometimes the decimal values do not drop to "10" and then you do not have to multiply by 10., etc.
Gene Wengert, forum moderator
For more info, see Log Volume