The strength of wood increases as its density increases. When evaluating the density of wood, the level of moisture in which its mass and volume were measured must always be known. Most commonly the density of wood is given as dry air density, whereby the mass and volume of the wood are measured with its level of moisture at 15% (or 12%). Density is often also given as a dry-fresh density, whereby the mass of the wood is measured dry, and the volume saturation point (about 30%) at a high level of moisture. The main tree species in Finland are pine, spruce and birch. Pine and spruce are the most common in construction. The density of Finnish pine is 370 – 550 kg/m3, spruce 300 – 470 kg/m3 and birch 590 – 740 kg/m3.
