If you are talking about water at standard temperature and pressure, 1 cubic meter = 1000 liters (1cc = 1 ml & 1000cc = 1 liter & 1 m^3 = 1,000,000cc) Multiply 399 x 1000 to convert to liters. 1 liter = 1 kg, so answer is also kilograms. If you are talking about the tonne (long ton or European ton) 1000 kg = 1 tonne. So divide answer by 1000. If you are talking about the short ton ( 2000 lbs U.S.) Then 1 kg = 2.20462262185 lbs. Multiply 399 x 1000 x 2.20462262185 and divide answer by 2000