Laser measures, ultrasonic tapes, smart tapes

Every few months a new gadget gets suggested for this measurement, usually because it worked well for something else entirely. Almost none of them can do the two things this measurement actually requires: press to bone for length, and wrap a soft circumference for girth.

Laser distance meters

A laser meter reads the distance to whatever surface it is pointed at, from a fixed reference at the tool's own back edge. That works for a wall. It does not work here, because the reading depends on holding the tool at a precise, repeatable angle and distance from a landmark that is under skin, not on a flat surface the beam can land on square. There is also no way to press it to bone, which is the entire point of the standard method.

Ultrasonic measurers

Same family, different sensing method, same problem. An ultrasonic tool times an echo off the nearest reflective surface in its cone, which on a curved, soft, moving target gives an inconsistent point of reflection rather than a landmark. It was built to measure rooms.

App-connected smart tapes

A cloth or fibreglass tape with a Bluetooth sensor built into the case logs the length you pull out, which is a genuine convenience for a tailor keeping records. It solves data entry, not accuracy - the sensor cannot tell you anything about tension, site, or whether the girth it logged was taken at midshaft. Girth taken with an ordinary tape at the right site and written down by hand is more informative than the same reading logged automatically at the wrong site.

Why "measures things precisely" is not the qualification

Each of these tools is precise at the task it was designed for. None of them was designed to find a bone landmark under a fat pad, hold pressure without compressing tissue, or wrap a tape snugly around something that moves. Precision on the wrong task is not accuracy on this one - the same gap that separates a photograph run through an AI model from an actual length: the model is precise at recognising an image, which is a different task from measuring one.

What to use instead

A rigid ruler for length, a cloth tape for girth, both used with the technique covered in full here. Neither is a gadget, and that is the point - the measurement rewards technique over hardware, which is also why a coarse numeric score from an image-based tool or a subjective read from a human judge will never converge on this figure however good the sensor or the eye: they are not measuring it, they are estimating something adjacent to it, which is also all a rating site like Rate Cock is claiming to give you. If what you want is a number in centimetres, the plain instruments still win.