I fourth it! Armorsmith is good for helmets, but I've had some issues with body parts (like my longer than average arms)
Some 3D print files are good right off the bat (like the ODST one in my profile pic), but another thing I've done to check measurements was to load the helmet file into a slicing program like Cura along with a 3D print file of a ruler that measures centimeters (cm). Then I just rotate and move the ruler around to make sure its good for me. Mainly around the openings of pieces, like the holes for your limbs