Measuring your coat size accurately is essential for a proper fit. Here's a guide to help you determine your coat size.
What You'll Need: A flexible measuring tape; A helper (for more accurate measurements); A pen and paper to record measurements.
Steps to Measure Coat Size:

Stand straight with your arms relaxed at your sides.
Wrap the measuring tape around the fullest part of your chest (under the armpits).
Keep the tape snug but not tight, and ensure it's parallel to the ground.
Record the measurement in inches or centimeters.

Measure around the narrowest part of your natural waist (usually just above the belly button).
Keep the tape comfortably loose (you should be able to fit a finger inside).

Measure around the fullest part of your hips (about 7–9 inches below the waist).
Keep the tape parallel to the floor.

Bend your arm slightly at the elbow.
Start at the center back of your neck (base of the collar).
Measure over the shoulder, down the arm to the wrist bone (where the coat sleeve should end).

Measure from the edge of one shoulder (where the arm meets the torso) to the edge of the other shoulder.
Keep the tape straight across the back.

For a short coat, measure from the base of the neck to the waist.
For a hip-length coat, measure to the top of the hips.
For a long coat (trench/overcoat), measure to mid-thigh or knee.

Once you have your measurements, compare them to a standard coat size chart (sizes may vary by brand).