Well, basically the same way any other army would. Most soldiers fell within a normal range of size, with the average combatant being 5'8" and weighing about 140 pounds. The US Army issued uniforms in stock sizes that would fit most soldiers and placed special orders with their clothing depots for unusually large or small soldiers. Jackets, fatigue blouses, and coats came in sizes I through IV, with I corresponding to a 36-inch chest and IV to a 42-inch chest; likewise, trousers came in four sizes, with the smallest fitting a 32-inch waist and the largest a 38-inch waist. They seem not to have been as concerned about height - if the garment was a little too long, the soldier could alter it, and if it was a bit too short, that wouldn't be too big of a deal..