Abstract Volume increment efficiency (VIE), a measure related to radiation use efficiency, is defined in this study as the annual total stemwood volume increment divided by the amount of global shortwave radiation intercepted by tree crowns during the photosynthetic season. We examined the influence of ecosite and of stand density on the VIE of Picea mariana in northern Ontario, Canada, using two data sets. The VIE of P. mariana differed significantly among ecosites, ranging from 0.071 dm 3 GJ −1 on poor-quality peatland sites to 0.345 dm 3 GJ −1 on fertile mineral soil sites. The VIE of P. mariana increased with increasing stand basal area and generally decreased with increasing radiation interception by individual trees, likely because allocation to branches is less in small trees and dense stands. VIE represents a straightforward way to relate volume growth to radiation interception in individual tree growth models.