How to Measure Your Tween or Teen
Boys 8–20 covers numeric sizes 8 through 20, letter sizes S/M/L/XL/XXL (used mostly by activewear and licensed sports brands), and denim brands that label by waist measurement in inches. Because boys in this range grow through length before width, measurements are a better guide than age. Take measurements over light clothing with the tape level and snug.
Chest: Measure around the fullest part of the chest, keeping the tape level under the arms. The primary measurement for tops, athletic tees, and outerwear.
Waist: Find the natural waistline — just above the hip bones — and measure there. Used for bottoms, shorts, and swim trunks. Note: boys often wear pants lower than the natural waist, but sizing charts assume the natural line.
Hip / Seat: Measure around the fullest part of the hips and seat, feet together. Useful for pants that fit closer through the seat, like joggers and slim-cut denim.
Height: Stand straight against a wall, heels flat and barefoot. Measure from the top of the head to the floor. Drives sizing on long-torso pieces like button-downs, dress shirts, and one-piece rashguards.
Inseam: Measure from the crotch seam down to the ankle while standing straight. Critical for jeans, chinos, and athletic pants — especially if he's tall or short for his age.
Denim Waist (inches): If a denim product is labeled 28, 29, 30, etc., that's the waistband measurement in inches — use the waist measurement above. If his waist is between two sizes, go up one; boys' denim often has little give in the waistband.
Pro tip: Activewear brands (Adidas, Nike, Under Armour, Johnnie-O, Psycho Bunny) tend to cut slim and athletic. If he's between sizes or likes room to move, size up one.
Pro tip: Boys in this range usually hit height milestones before width. If his height puts him in a larger size but chest and waist don't, prioritize length — hems are easy to cuff; sleeves and inseams aren't easy to extend.
Pro tip: For licensed sports apparel, the letter-size chart is the default. Match his chest measurement to the chart — the letter sizes run smaller than adult S/M/L/XL.
