Dimensional measurement of internal profile is conventionally performed mechanically with instruments like vernier calipers. Here, we cope with the measurement by using an optical caliper. The caliper consists of a semiconductor laser, a right conical mirror, a lens system, and an image sensor. The concept of the measurement approach is intersecting the object with a disk light sheet, collecting the cross-sectional profile image with an image sensor, and extracting dimensions of the profile. Example of practical measurement is presented.