864 cubic inches ÷ 139 = 6.22, rounded up to 7 lb for UPS Daily Rates and FedEx. USPS bills actual weight because the box is not larger than 1 cubic foot.
How heavy does a 12x12x6 box need to be to avoid DIM charges?
With UPS and FedEx, anything packed under 7 lb is billed as 7 lb. Above that, you pay actual weight.