-The allometry of bark thickness was estimated both from thickness data taken with a bark gauge only on ridges and from cross-sectional area data based on a contour of the outside bark-surface, together with an estimate of the inside bark-boundary. Three alternatives of the contour method are presented; they differ in how the outside bark-contour is obtained, in how the inside bark-boundary is estimated and in invasiveness. Unlike the contour method alternative (CM2) with equivalently low invasiveness, the bark gauge method significantly overestimated mean bark thickness and overestimated it more for larger individuals. Because the bark gauge method led to significantly and inconsistently higher allometric coefficients than the contour method, the contour method is more appropriate for comparative and ecological studies of bark allometry.