1x Board Sizes These boards lose 1/4 inch in thickness and 1/2 inch in width before leaving the mill. That means a 1 x 4 board is actually 3/4 inches by 3 1/2 inches.Click to see full answer. Similarly one may ask, how big is a 1×4 board? Nominal vs. Actual Measurements of Dimension Lumber Nominal Size Actual Size 1 x 6 3/4 x 5 1/2 inches (19 x 140 mm) 1 x 8 3/4 x 7 1/4 inches (19 x 184 mm) 1 x 10 3/4 x 9 1/4 inches (19 x 235 mm) 1 x 12 3/4 x 11 1/4 inches (19 x 286 mm) Also, is a 4×4 really 4 inches? Believe it or not, there actually is some rhyme and reason for why the actual measurements of dimensional lumber don’t 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 Besides, how thick is a 1×6? A 1×6, for example, actually measures 3/4″ x 5 1/2″.How thick is a 2×4?A piece of surfaced (sanded smooth) 2×4 lumber actually measures 1½ inches thick and 3½ inches wide. In rough-cut condition, a 2×4 is slightly less than 2 inches thick and approximately 4 inches wide. When wood is milled from a rough to a smooth surface, it loses about ¼-inch from each of its four sides.