What is the actual measurement of a 2 by 4?

Answer 1

That depends on what wood it is made of and how much it has dried when you measure it. In Sweden the cutters to plane "2 by 4" s are set at 45 mm and 90 mm distances when planing kiln dried wood for interior construction work. These boards are usually planned from raw cut timber that was cut using settings of about 50 and 100 mm.