The density is the ratio of the substance's mass to its volume. Assuming that the wood is a rectangular block, the volume would be equal to
Volume = LWH
where
L is the length, W is the width and H is the height
Volume = (4 in)(6 in)(20 in) = 480 in³
Since 1 foot is equal to 12 inches,
Volume = 480 in³ * (1 ft/12 in)³ = 0.278 ft³
Thus, the weight is equal to
Mass = 7.8 lb/ft³ * 0.278 ft³ = 2.167 lb
Since 1 kg = 2.2 lb,
Mass = 2.167 lb * (1 kg/2.2 lb) = 0.985 kg
