An arrangement and method for measuring a piece of timber in a wood handling machine, wherein the piece is grabbed by a cutting head arranged to a set of booms in the wood handling machine, and the dimensions of the piece are measured by at least one measuring device in the wood handling machine. A measuring signal field formed by one or more measuring beams is also directed to the piece of timber with a monitoring device utilizing contact-free measurement, and a point cloud to be stored is provided by the measuring signal field it produces. The parts to be identified are identified from this point cloud, and a quantity to be measured is defined and formed of the information content of the point cloud. The obtained result is directed to a measuring system in the wood handling machine for further utilization.