Metric Framing Material Sizes

• While working in countries that use the metric system, woodworkers will likely refer to lumber using common American names. For instance, a standard framing member that measures 90mm by 45mm is typically referred to as a two-by-four. Even in the United States, a two-by-four isn't 2 inches by 4 inches (it's actually 1-1/2 inches by 3-1/2 inches), but it's still called a two-by-four. A piece of lumber typically called a two-by-six should measure about 140mm by 45mm.
  
  

Metric Plywood Sizing

• In the U.S., sheets of plywood are typically sold in 4-foot by 8-foot sheets (of varying thicknesses). In countries that use the metric system, sheets of plywood are sold in 1200mm by 2400mm sheets, which is a little smaller than the plywood sold in the U.S. Keep this in mind if you're converting plans from metric to standard measurements or vice versa. Check with your lumber supplier on the exact sizing of your material while planning your project.
  
  

Surfacing

• In the U.S., most softwoods are sold as S4S, which means surfaced on four sides. Hardwood in the U.S. is typically labeled as S4S, S2S (surfaced on two sides) or rough-cut. In most other countries, though, lumber that's surfaced on all four sides would be referred to as D4S (dressed on four sides). It's a subtle difference, but one that you'll see on many woodworking plans that feature metric dimensions.