Stand upright with your shoulders relaxed
Locate the outer edge of one shoulder
Measure straight across the back from one shoulder edge to the other shoulder edge
Keep the tape measure level and parallel to the floor
Record the measurement in inches or centimeters
For a garment shoulder measurement, measure from the shoulder seam on one side to the shoulder seam on the other side
For a body shoulder measurement, ask someone to help for better accuracy
Double-check the measurement to confirm accuracy