Resumo. ABSTRACTThe aim of this paper is to verify the accuracy of the optical dendrometers Criterion 400 and RC3H bystudying the quality of measures of wood volume determination of standing trees through these dendrometers.The study was developed at the Experimental Station of Forest Sciences, in Itatinga, São Paulo state, whichbelongs to the University of São Paulo (ESALQ / USP). It was sampled a total of 175 trees in three plots ofEucalyptus grandis. The stem diameter of standing trees was measured by the two optical dendrometers atdistances of 0.1, 0.4, 0.7, 1.0, 1.3, 2.0 meters from this point meter by meter along the stem up to 8 metersheight. After measuring the standing trees they were felled and the diameter was obtained in differentpositions with a caliper and a tape in the same positions that the non-destructive measures were taken. Withthe diameters the volume was calculated by section and by individual trees by the Smalian formula forthe comparison of methods. Analyzing the measurements of stem diameter and the individual tree volume realizes that the two dendrometers provided measures generally underestimated. However, the Criterionprovided the best estimates. For the diameter and individual tree volume the Criterion showed underestimatederrors averaging approximately 1 cm (10%), while the RC3H resulted in errors greater than 5 cm (30%) onaverage.Thus, when measuring observed variables in a non-destructive way with reliability and accuracy,the Criterion showed better results.