The bulk or gross density determines the dead-weight load of the building material. Wood contains varying amounts of water depending on whether the timber is freshly cut, has already dried a little since being cut or whether the wood has been dried to wood equilibrium moisture content for indoor use. Wet wood is the heaviest. Since the mass of the wood depends on the wood's water content, the gross density is dependent on the wood moisture content.
The gross density is indicative of the ratio of cell wall material to hollow space in the wood. It is a ratio that needs to be calculated. The gross density „p“ of wood, timber products and wood-based materials is the ratio of the mass „m“ to its volume „v“.
Gross density = mass of the wood / volume of the wood in kg/m³ or lbs/cu.ft
Examples based on a wood moisture content of 12-15%:
balsa wood 90–260 kg/m³, spruce 430–470 kg/m³, bangkirai 650–1,160 kg/m³, ipe (Brazilian walnut) 950–1,150 kg/m³
The range of the gross density is also dependent on the location-specific and environmental factors of the wood, e.g. the origin of the tree (e.g. Asian continent).
The differences in gross density within a wood type can be seen from the respective differences in the width of the growth rings in the wood.