Lumber weight calculator
Specific gravity counts the wood ovendry. The board in your hands is not ovendry, and leaving out the water is why published weight calculators come in light.
The missing term
Specific gravity is a ratio against water and has no units. Crucially, it is always referenced to the ovendry mass of the wood — the weight with all moisture driven off. So converting it to a weight per cubic foot takes more than multiplying by 62.4, because the board you are lifting has water in it that the ovendry mass never counted.
The correct form multiplies by one plus the moisture fraction. The Handbook works the example itself: white ash at 0.605 specific gravity has an actual density of 42.2 pounds per cubic foot at 12% moisture content. Multiply 0.605 by 62.4 and stop, and you get 37.8 — ten per cent light. Reach for the green-volume specific gravity by mistake and you get 34.3, nineteen per cent light.
Both of those errors are in circulation on pages that exist specifically to help people plan a load. Weight errors always run the same direction, and the consequence of underestimating a load is more interesting than the consequence of overestimating one.
Why some species return no answer
The Handbook reports specific gravity on two different volume bases. Domestic species get volume at 12% moisture content; imported species get green volume. Those differ by around 10% on average, and moving between them needs a shrinkage relation this site has not independently verified.
So for teak, ipe, purpleheart and the other imports, this tool declines. It would be trivial to apply a plausible conversion and return a confident number that is quietly a tenth wrong, which is the exact failure this whole site was built against. An explicit refusal is more useful than a wrong figure that looks right.
Weight changes with the season too
Everything above assumes 12% moisture content, the standard basis for published figures and a fair assumption for kiln-dried stock that has been indoors a while. Green timber is a different animal. Green western redcedar sapwood averages 249% moisture content — the water outweighs the wood two and a half to one — and even ordinary green oak runs 60% to 80%. A pack of freshly sawn boards can weigh nearly twice what the same pack will weigh a year later.
Asked at the bench
Is specific gravity the same as density?
No, and the distinction matters here. Density has units — pounds per cubic foot, or kilograms per cubic metre. Specific gravity is that density divided by the density of water, which cancels the units and leaves a bare ratio. Several published pages use the two words interchangeably, which is how the conversion step goes missing.
Which figure do I use for shipping?
The 12% one, unless the timber is genuinely wet. Kiln-dried stock that has been stored indoors will be close to it. If you are moving green or air-drying timber, weigh a sample rather than calculating — the moisture content range is far too wide for an estimate to be useful.
Does the species table’s specific gravity match the wood database I use?
Possibly not, and it repays knowing why. Some references publish specific gravity on a 12% mass and 12% volume basis, which is not the same quantity as the Handbook’s ovendry mass over 12% volume. Two tables can both be right and still disagree, so check what each one is measuring before comparing them.
Why does thickness use the rough figure here?
Because it is consistent with how the boards were tallied. If you want the weight of surfaced stock, the difference is real — 4/4 planed to 13/16 has lost 19% of its volume, and its weight with it.