5 1/2 inches on each side. The longest it goes is 7 1/4. The part with the soft covering on the straps that go behind his shoulder blades onto his back are at smallest 8 1/2 inches. At longest 18 3/4. This is adjusted by a toggle button and extending the "rope". In between the front measurement and the rear there is a netting that goes on the chest and that measures 5 inches long. I HOPE THIS HELPS WITH SIZING.