imported post
In as-cut lumber, 12'' x 4'' x 2'' = 96 in^3 = 0.056 ft^3 Pine is about 30 lb ft^-3, depending on species and moisture content, so ~1 2/3 lbm.
Further, '2 x 4' is more usually dimensioned lumber = 1-1/2'' x 3-1/2'. So a 12'' piece would weigh less, being only 63 in^3, about a pound.