The option has in hidden mode. Not able to measure the model. Kindly suggest me to measure the model. I don't have any original 3D models to measure.
Since measure has been disabled - take screen captures of Front, Top and Side (and maybe bottom and another side). Decide on a logical dimension for one of the edges. Scale all images based on this decision. Sketch over the images. (I do this on separate sketches so that I do not accidently move the image(s).)