Buying
lumber in the international market requires sometimes conversions from
cubic meter into linear meter or square meter and dealing with US
orientated measuring system you will come across BFT (board feet) and sqft
(square feet) the following is outlining which one is which:
Rough sawn wood boards
A
board foot measures one square foot that is one inch thick. A cubic foot has 12 board feet. So, to figure out board feet in rough sawn
lumber, you multiply the thick (inches) by the width (inches) by the length
(in feet), and divide by 12. The
formula would look like this:
(Thickness * width * length) / 12
A
1" x 6" x 8' (=1x6x8=48/12) would have 4 board feet.
Buying and selling logs
When
it comes to trees, there are several ways to measure them. You can use a cubic foot volume (not
used much), a cord volume (which has 128 cubic feet on a standard cord), by
the ton, or by the board foot. None
of these are really transferable in the mathematic sense from one to the
other.
To
top things off, there are several types of scales used to determine the
amount of board footage in a tree or a log. You will see terms like Doyle, Scribner, and International
scales used in various threads.
They estimate volume, and you can't say that so many feet in Doyle
is equal to so many feet in Scribner.
Which scale is used varies from one place to the other.
Overrun and underrun in milling
The
next problem is that 1,000 board feet in tree scale will have more footage
in log scale, even using the same scaling techniques. And, you will normally cut more lumber
out of a log than what it scales at.
They call that overrun. If
you go under, its called underrun.
Commercial and (FSC) official log measuring
In
Bolivia there is two types of measurements, one is commercial (without the
sapwood and holes) and the other is according to the authorities, including
sapwood and bark. Since a log is conical, there are two ends of the logs
which are not equal in diameter. The end closer to the top is less in
diameter and the end closer to the ground is wider in diameter. Using the commercial
way of measuring the calculation is the following:
diameter 1 in cm x diameter 2 in cm x length in
cm x 0.7854 and everything dived in 1,000,000
so if your log is 44cm x 47cm (excluding holes
and sapwood) x 400cm, the volume of this log is 0,650m³
using the measurement
used by the authorities the difference is that you need to measure both
ends of the log and include the sapwood and the bark (we take for this
example the same log):
log end 1: diameter 1 in cm x diameter 2 divided
in 2
x
log end 2: diameter 1 in cm x diameter 2 divided
in 2
x
length x 0.7854 = volume of the log.
Example: 49cm x 53cm/2 x 54cm x 66cm/2 x 400cm x
0.7854 = 0.961m³
it is obvious that
using the second method which included the sapwood and bark turns out to be
more in volume m³.
