Nominal vs. Actual Lumber Sizes

Date:10/31/2017
Author:Terry L.
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What Is a 2x4's Real Size?

Lumber depth and width are typically given in “nominal” dimensions, but those aren’t the true sizes. Which means, for example, three 2x4 boards laid side by side will not measure a foot across. Because a nominal 2x4 board is really 1-1/2 inches by 3-1/2 inches. More or less.

When I learned this, my first thought was what is this nominal nonsense and why is it even a thing? Keep reading, or skip to these handy “actual vs. nominal” size charts.

The difference between nominal and actual dimensions

The nominal dimension is a board’s size when first cut, before it’s been planed (aka “surfaced”) and dried. Technically, after planing and drying, the board should meet a standard final dimension, the “actual” size.

So why don’t lumberyards just skip the nominal ridiculousness and simply state the actual sizes?

via GIPHY

Here’s the reason. A nominal 2x4 board starts its life 2 inches by 4 inches. Then, its edges are surfaced, reducing its width and depth. Then, the freshly cut board dries, ending up an actual 1-1/2 inches by 3-1/2 inches.

The final-final measurement can change, because wood is hydroscopic – it absorbs and releases water into the air. And different woods dry at different rates. And the same boards stored in a hot, dry lumberyard will likely be a bit smaller, while those in a humid location could be a tad larger. And if the humid location suddenly has a dry spell, then those boards will shrink slightly. And what if they’re stuck in the pile for months? Or the sawmill person shaved a bit more off that one time?

It’s way easier to just say 2x4.

But wait - another complication.

Softwoods vs. hardwoods: There’s a difference

Actual sizes for softwoods and hardwoods are NOT the same – and standards differ. Softwood nominal dimensions include length and thickness, while hardwood nominal dimensions are for thickness only. Actual thickness size depends on whether the board has been planed on one (S1S) or both (S2S) sides.

I’ll spare you the long explanation for this. Just check out these charts showing the nominal and actual measurements for both softwood and hardwood.

This is legal?

Some people get a little maniacal about nominal vs. actual dimensions and wonder if it’s even legal. Yep, it is. According to the American Wood Council, the National Institute of Standards and Technology permits stores to label lumber with nominal dimensions as long as the label or other sign clearly states that the size given is a nominal size and also states “the actual or minimum measurements.”

Currently, state and local inspectors don’t have standard rules to follow when checking these dimensions. So, you’ll have to verify these yourself, if exact measurements are important to your project.

Don’t leave the house without your tape measure.

Don’t stress out about nominal and actual numbers. If preciseness matters, I recommend that you stay chill and take a tape measure when you head to the lumberyard to buy boards. Check widths and thicknesses before making a purchase for fewer surprises after you start your project.


Actual Lumber Size Chart for Softwoods*

*If you need precise measurements, measure wood before buying. Chart source

 Nominal Depth x Length

Actual Depth x Length 

1×2 ¾" × 1½"
1×3 ¾" × 2½"
1×4 ¾" × 3½"
1×6 ¾" × 5½"
1×8 ¾" × 7¼"
1×10 ¾" × 9¼"
1×12 ¾" × 11¼"
2×2 1½" × 1½"
2×3 1½" × 2½"
2×4 1½" × 3½"
2×6 1½" × 5½"
2×8 1½" × 7¼"
2×10 1½" × 9¼"
2×12 1½" × 11¼"
4×4 3½" × 3½"
4×6 3½" × 5½"
6×6 5½" × 5½"

Actual Lumber Size Chart for Hardwoods*

*If you need precise measurements, measure wood before buying. Chart source

 Nominal Thickness

Surfaced 1 Side (S1S) 

Surfaced 2 Sides (S2S) 

¾" 58 916
1" 78 1316
1¼" 118 1116
1½" 138 1516
2" 11316
3" 21316
4" 31316

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