Also in North America, hardwood lumber is commonly sold in a quarter system, when referring to thickness; 4/4 (four quarter) refers to a 1-inch-thick (25 mm) board, 8/4 (eight quarter) is a 2-inch-thick (51 mm) board, etc.

Similarly, what is the actual size of a 4x4? Nominal vs. Actual Measurements of Dimension Lumber

Nominal Size Actual Size 2 x 12 1 1/2 x 11 1/4 inches (38 x 286 mm) 4 x 4 3 1/2 x 3 1/2 inches (89 x 89 mm) 4 x 6 3 1/2 x 5 1/2 inches (89 x 140 mm) 6 x 6 5 1/2 x 5 12 inches (140 x 140 mm)
Also question is, is a 4x4 really 4 inches?

Believe it or not, there actually is some rhyme and reason for why the actual measurements of dimensional lumber dont match their names.

Actual Dimensions and Nominal Dimensions.

Nominal Measurement Actual (inches) Actual (mm) 2 x 12 1-1/2 x 11-1/4 38 x 286 4 x 4 3-1/2 x 3-1/2 89 x 89 4 x 6 3-1/2 x 5-1/2 89 x 140
How much does a 4x4 cost?

Ricky Beggs, editor at Black Book, researched a few pickup models for the cost variance between new 4x2 and 4x4 models at three years old. For new trucks, the MSRP premium for a 4x4 model is about ,200 to ,900. At three years old, the spread is ,000 to ,000.