Harness sizes are not standardised. A medium from one maker can be smaller than a small from another, and weight-based sizing on the packaging causes most of the returns. The reliable route is to measure the dog and read the manufacturer’s chart for the exact model.

This helper turns your measurements into a likely size band across typical retailer charts, shows which measurement should decide the size when the two disagree, and gives you the fit checks to run before the first walk.