Rear-Facing Harness: 4-40 lb, head must be at least 1" below headrest adjustment handle; Forward-Facing Harness: 22-65 lb, up to 49"; Highback Booster: 40-100 lb, 43-57", at least 4 years old; Backless Booster: 40-120 lb, 43-57", at least 4 years old