As per IS 1708 : 1969, determination of specific gravity; When only specific gravity is to be determined the test specimens shall be 5 × 5 cm in cross-section and 15 cm in length or 2 × 2 cm in cross-section and 6 cm in length. When rectangular specimens are not obtained, a specimen of about 10 cc volume shall be taken. 
The specific gravity of all the specimens for mechanical tests shall be calculated as; 

Where W₁ = weight in 'g' of test specimen, V₁ = volume in 'cm³' of test specimen and m = percentage moisture content of the test specimen. 
Size of timber used for specific gravity test is 50 × 50 × 150 mm.