Unbutton your shirt and spread it out on its front. Pull the collar so the collar band is straight. Place the end of the tape measure at the center of the button and measure in a straight line across to the outer edge of the button hole.

Lay out the buttoned shirt on its back. Make sure there are no wrinkles and that the fabric lies flat. Measure across on a straight line between both armpits, from the seam where the sleeve meets the body to the other side. Note that this is not a circumference measurement.

Again spread the buttoned shirt on its back. Make sure it is all flat and that there are no wrinkles. Identify the narrowest part of the waist and measure across. Note that this is not a circumference measurement.

Spread the buttoned shirt out on its back. Make sure it is all flat and that there are no wrinkles. Find the bottom of the side seams and measure across. This is not a circumference measurement.

Lay out your buttoned shirt on its back and make sure it is flat and without wrinkles. Put the end of your measuring tape at the top edge of your shirt as close to the collar as possible. Measure in a vertical, straight line to the bottom of the shirt.

Spread the buttoned shirt out on its front. Put the measuring tape at the outside edge of the seam, just above where the yoke meets the sleeve, and measure straight across to the same point on the other side.

Lay the shirt on its back. Straighten out the arm and remove any wrinkles. Measure from the inside edge of the seam where the upper part of the sleeve meets the body, and in a straight line to the end of the cuff.

Measure from the inside edge of the armpit seam, down in a straight line to the end of the cuff.

Spread your shirt on its back and pull the arm out so it lays flat. Make sure that the sleeve fabric near the body is flat and without wrinkles. Measure from the bottom edge of the sleeve near the armpit to the point where the upper sleeve meets the body.

Unbutton the cuff and lay it out flat with the button(s) facing upwards. Measure from the center of the button to the outer edge of the button hole.