My lovely enabler, Melanie

Balsa is one of the lightest woods available, and in many respects has the highest strength-to-weight ratio of any wood - even oak. The chart at the right gives a comparison of a few familiar wood types.

Hobby grade balsa is harvested in the jungles of Ecuador, kiln dried, cut into large blocks, and shipped to the U.S. for final cutting and sanding. Most balsa from hobby shops is in the 8-10 lbs/ft³ realm. The rock-hard stock that nobody wants is sent to the airplane kit manufacturers ;-)
 
Before being discovered as an ideal source of wood for model airplanes, balsa trees were cut and assembled into raft for floating down the river. In fact, the word "balsa" is Spanish for the word "raft." Balsa has been widely used by the military for air-drop pallets, and in fact, during World War II, balsa wood for models became scarce because the Army Air Force needed it for operations. Bamboo and other reeds were tried by modelers as a substitute wood, but it never could replace balsa.

The charts below for weights of standard hobby shop balsa sheets, sticks and blocks were calculated from a simple formula that takes the density of the of each piece of balsa and multiply it by the volume. For 48" lengths, multiply each 36" value by 4/3 (1.333).

Wood Properties Species Weight lb/ft3 Stiffness Strength Bending Strength Comp- ression Strength Balsa 8 72 70 75 Balsa 10 100 100 100 Balsa 14 156 161 149 Spruce 28 230 260 289 Yellow Pine 28 222 277 288 Douglas Fir 30 241 291 341 Hickory 50 379 638 514 Oak 48 295 430 366 Basswood 26 261 288 288 Black Walnut 37 301 506 512

Example:

A 3/16" x 3" x 36" sheet of balsa has a volume of 20.25 cubic inches (in³), which is equal to 0.01171875 cubic feet (ft³). A piece of balsa with a density of 8 lbs/ft³ is the same as a density of 128 oz/ft³. So, to find the weight of the balsa sheet, multiply 128 oz/ft³ by 0.01171875 ft³ to get 1.500 oz. A 48" length would weigh 1.500 oz. x 4/3 = 2.000 oz.