In this study, vulnerability to cavitation, P50 (i.e. the water potential causing 50 % loss of hydraulic conductivity), of Norway spruce trunkwood at different cambial age was related to wood density. Wood density was calculated from mass in the oven dry state related either to volume at the oven-dry state (dry wood density) or to volume at full saturation (basic wood density). Dry wood density and basic wood density were strongly linearly related (r² = 0.99); there was however a shift from the 1:1 reference line with increasing dry wood density. Dry wood density as well as basic wood density had similar high predictive qualities for P50 (r² = 0.85). The quadratic regression lines took however a quite different course below-4 MPa because volume shrinkage increased with increasing dry wood density. For Norway spruce sapwood with high dry wood density, mixing up different wood density traits would thus result in a predicted overestimation or underestimation of vulnerability to cavitation. Gravimetrically wood density measurements at different moisture contents (starting at full saturation) are easily to achieve on standard size specimens and the conversion curves obtained will be of high value for future ecological studies on other species and across species.