Exact definitions: 1 in = 25.4 mm, 1 lb = 0.45359237 kg, 1 US gal = 231 cu in, 1 acre = 43,560 sq ft, 1 ton = 2,000 lb (NIST). Weight converts to weight only; it does not convert a volume of material to its weight. Estimates only. Check measurements, product labels and local building codes before you buy or build.