whats the correct way of calculating a slab volume?

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Forum topic by Greedo posted 02-06-2011 12:06 PM 950 views 0 times favorited 4 replies Add to Favorites Watch
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473 posts in 2925 days

02-06-2011 12:06 PM

hey all, i buy my hardwood usually in rough slabs (with the bark on both ends)
i don’t know how it works in the states but overseas hardwood is sold by the cubic volume, not by length.
so for each slab they measure the average width, multiply by length and thickness (all in meters) and then multiply by the cost/cubic meter. then you have the price.

on the slabs i used to buy they had marked the width on the slab in blue spray from the mill, the slabs i get now come without marking and it’s the guy from the yard that measures them, and i am wondering if he is doing it right.
it seems like they measure the widest part of the slab without bark, at around 1/4th of the height.
while i heard you need to measure at 3/4th of the height, the smallest width without bark.

with widest or smallest i mean the up or down side of the slab where you have the most or fewest bark, since it’s not quartersawn it can on some slabs devide in two the usable part of the slab.

when i measure with both methods i get a difference of 20%.
it is not so much about only paying for the “usable” part of the slab, but with their method i feel like i am paying for more volume than there actually is, including the waste.

anybody know the correct method?

4 replies so far

View crank49's profile


4030 posts in 2935 days

#1 posted 02-06-2011 03:34 PM

I am not clear about the way you explained their method. Your first statement was exactly true; average width x length X height is equal volume. I suppose one way to check if their number is 20% high would be by weight. If you look-up the density of the species of wood you are buying and multiply that density by the claimed volume, you should have a weight number to compare to actual weight. A 20% variance would be obvious in the weight as a comparison check. Of course, moisture content could add another variable, but still you should have an indication if they are ripping you off.

View Sawkerf's profile


1730 posts in 3033 days

#2 posted 02-06-2011 04:01 PM

I don’t know if there is a “correct method”. Have you taken your own measurements and questioned them about the differences between yours and theirs?

-- Adversity doesn't build reveals it.

View CharlieM1958's profile


16274 posts in 4183 days

#3 posted 02-06-2011 04:23 PM

It just sounds like typical salesmanship to me. You know…. kind of like the way they will keep charging the same amount at the grocery for a container of ice cream, but the container keeps getting smaller. So the suppliers you are talking about are probably tweaking the way the measure their slabs in order to keep the cubic volume unit price from changing too drastically.

-- Charlie M. "Woodworking - patience = firewood"

View Scsmith42's profile


125 posts in 2641 days

#4 posted 02-06-2011 07:58 PM

I don’t think that there is any single “correct” method, which is one reason why the prices vary. Probably the best thing to do is to ask the seller how they measure the volume, and if there is a discrepancy bring it up to them.

Here in the States we usually sell based upon board footage (144 cubic inches). However, there are differences in terms of “green measure” versus “dried” measure, since the wood shrinks as it dries. Some sawyers reference the green measure, even if the board has shrunk below it. Others the dry measure, but they usually charge slightly more.

Measuring can vary – some millers exclude any defects in a board/plank from their measurement calculation, others use the overall total. There is no single standard that I”m aware of.

-- Scott, North Carolina,

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