Glossary:
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When measuring the density of wood a ratio called specific gravity is used. Specific Gravity is a comparative measurement of a materials density to that of water. Water is used as a base line for specific gravity and is given a value of 1. All other materials are compared to water and expressed as a ratio heavier or lighter in density. As specific gravity is a comparison tool, it can be applied across any units of any material. The density of pure water is 62.4 lbs/cu.ft (pounds per cubic foot) and if a sample of apple lumber has a specific gravity of 0.73 then we can calculate that its density is 0.73 x 62.4 = 45.552 lbs/cu.ft. Note, kg/cu.m divided by 16.01846 = lbs/cu.ft. While this measure is similar to lbs/cu.ft. it is good to know the meaning of this measurement as it is commonly used in the timber/lumber industry to describe wood characteristics. 
For more on the mathematics of specific gravity, Click Here |