Step 1: Measure rib cage
Keeping the measuring tape parallel with the ground, measure around your rib cage directly under your bra. Round all fractions to the nearest whole number. For example, if the tape measure reads 29.5 inches, round this number up to 30 inches. If the measurement is even, add 4 inches. If the measurement is odd, add 5 inches. According to the picture shown, her band size will be 34 inches.