I just do l x w x h and divide by 231.
Example: 48 x 12 x 21= 12096 / 231 = 52.36g its a little off since its not exact dimensions but it get you in the ballpark.
Example: 48 x 12 x 21= 12096 / 231 = 52.36g its a little off since its not exact dimensions but it get you in the ballpark.
