US Lumber measurements

Hi everyone.
I recently purchased some wood project plans from the USA and just want to clarify the way in wich many of the measurments are given. Lumber is shown as 4/4, 6/4, 3/2 8/2 etc. would these sizes just be 1" for 4/4 - 1.5" for 6/4 and so on. If so, why on earth do they use these silly fractions in place of simple fractions (did you see what I did there?)? The only other reason I can think of is giving the two dimensions which we would call 4"X4" etc. Can any one shed some light on this as I dont want to purchase the incorrect sizes

I know not why, but the US refer to timber sizes in fractions and you are correct to read 4/4 as four quarters or one (inch as they are also imperial measurements).
Stay safe, Philip.

Hello, in my experience woodworkers in the USA seldom use fractions or metric dimensions when describing their wood plans. Whereas here in the UK we talk of a piece of wood or timber (never lumber which means something else) as being four by two (4 by 2 inches) in the USA they always give the smaller number first. The way those dimensions were written for example 4/4 means 4x4 (four inches by four inches or 3x6 (three inches by six inches). Fractions when sometimes used are generally sixty fourths, thirty seconds or sixteenths of an inch and are written differently to the larger dimensions describing timber, I hope this is of use.

Americans will only use imperial measuring. They laugh at our usage of the metric system. All the numbers they use are in inches.

I always find it amusing that we buy timber in metric lengths but with the cross-section measured in inches. When I was in Germany, they did the same, except that it wasn’t labelled as “2 by 1” - it was “50 by 25” mm! That was several decades ago, so they might now use 20, 30, 40, etc rather than 25.

Hi everyone and thanks for the information. I just discovered this article which seems to simplify everything. Hardwoods are measured in quarters in the USA.

1/2" inch 3/8 inch (9.5 mm) 5/16 inch (7.9 mm)
5/8" inch 1/2 inch (13 mm) 7/16 inch (11 mm)
3/4" inch 5/8 inch (16 mm) 9/16 inch (14 mm)
1" = (4/4) inch 7/8 inch (22 mm) 13/16 inch (21 mm)
1 1/4" = (5/4) inches 1 1/8 inches (29 mm) 1 1/6 inches (27 mm)
1 1/2" = (6/4) inches 1 3/8 inches (35 mm) 1 5/16 inches (33 mm)
2" = 8/4) inches 1 13/16 inches (46 mm) 1 3/4 inches (44 mm)
3" = (12/4) inches 2 13/16 inches (71 mm) 2 3/4 inches (70 mm)
4" = (16/4) inches 3 13/16 inches (97 mm) 3 3/4 inches (95mm)

Hardwood may be sold in quarters. Each quarter refers to 1/4 inch of thickness, meaning that a 5/4 board is roughly 1 1/4 inches thick. If your project calls for a piece that is exactly 1 inch thick, you’ll want to purchase a 5/4 board and mill it down to the proper size using a jointer/planer.

Hardwoods are rarely sold in standard dimensions the way softwoods are. Instead, suppliers generally sell hardwoods in a unit of volume known as the board foot. One board foot is equal to 144 cubic inches of wood. In other words, a board that is 1 inch thick, and 12 inches wide and long contains one board foot of hardwood lumber.

How simple is that? In the USA you have yards, feet, inches 1/4’s, 1/8’s, 16’s, 32’s, 64’s and so on. Now to simplify it further they also use 1/4’s on hard woods for timber over 3/4’s.
Are you sure they are laughing at us and not crying?

Hi. This online calculator may come in handy for your wood calculations.

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