.....................And just so anyone might want to know, the density of water at 20°C (68°F) is 62.4 lb per cubic foot.

I am a fan of the metric system, especially in less-than inch measurements. Another plus for the metric system is specific gravity is an easy calculation and it is a unitless measure. Whether your usual method of measuring is metric or Imperial specific gravity is outside the units of these measuring systems.
I do not know how metric weights and volumes work out so perfectly for specific gravity. I don't need to know how but it does.
To determine specific gravity you measure length, width and thickness of a piece in millimeters. Multiply all three measures together to determine volume. Then, divide the weight in grams into the volumetric figure. Once you have this figure, divide it into 1. The decimal point will have to be moved since we calculated in millimeters and kg/m3 is the equivalent of specific gravity.
The net positive is specific gravity is unitless and therefore universal across all measuring modalities.
Maybe it is too much to hope for that suppliers will list the specific gravity of individual soundboards (in particular), but at least a boy can dream.

Why use specific gravity instead of density?

I do not know how metric weights and volumes work out so perfectly for specific gravity. I don't need to know how but it does.
.

Why use specific gravity instead of density?

It works out so perfectly because grams are a metric measurement. 1 gram = weight of 1cc of water (originally at STP, then 4 degrees C, now somehow related to Planck's constant )
S.G. = mass/unit volume
Density = mass/ unit volume
S.G. = Density
The reason to use S.G. instead of imperial units (psi, pounds/cu.ft.,tons/cu. yd.) is because it is a unitless measurement it makes calculations easier to do in your head.

1 gram = weight of 1cc of water (originally at STP, then 4 degrees C, now somehow related to Planck's constant )

Any way you calculate it, it's a great way to choose specific tops with particular purpose...

Clay, in you formula above your calculating density not specific gravity. You can calculate density in metric units too. To get specific gravity you divide the density by the density of water which gives a ration of one mass to another.
The density calc is all you need as you point out, if you use grams and cc's you get a number very close to the Specific gravity (waters not quite 1g/cc)
It's not correct however to say the SG = Density, splitting hairs, I know.

I’m an amateur marine aquarist if 16years.
I use a refractometer


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