Actual lumber sizes: why a 2x4 isn't really 2 by 4

If you've ever stood in the lumber aisle with a tape measure, convinced the store mislabeled every board, you're not alone. Actual lumber dimensions are one of the first things that trips up new woodworkers, and it's a costly surprise: cut a project from the "names" instead of the real sizes and your joints won't line up, your shelves won't fit and you'll be back at the store for more wood.

This guide gives you a full nominal vs actual lumber size chart, explains why the sizes shrink, and shows how to avoid the mistakes it causes.

Lumber size chart: nominal vs actual

These are the standard dressed (dried and planed) sizes for softwood lumber sold at US home improvement stores. Measurements are thickness x width.

Save or print this chart and keep it in the shop. It's the one reference you'll check more than any other.

Why a 2x4 isn't 2 by 4

A 2x4 isn't short-changed on purpose. The missing half inch disappears in two steps between the sawmill and the store.

1. Drying shrinks the board

When a log is first sawn, the boards are cut close to their full nominal size. That fresh, or "green," wood is full of water. As it dries, in a kiln or in the open air, it shrinks across its width and thickness. Drying matters: wet lumber twists and cracks as it dries out in your project, so drying it first gives you a more stable board.

2. Planing smooths and standardizes it

Rough-sawn boards have fuzzy, uneven faces. The mill runs them through a planer that shaves every side smooth. That makes the wood nicer to handle, and it makes every 2x4 the same size as every other 2x4, which is what lets builders, and plans, rely on it.

Sizes weren't always consistent. Mills once cut to their own sizes, and the industry only settled on shared standards in the 1920s. Today's dressed sizes come from the American Softwood Lumber Standard, which is why a 2x4 from one store matches a 2x4 from another.

The quick rule to remember

You don't need to memorize the chart. For standard softwood lumber:

• Thickness: 1-by boards are ¾", 2-by lumber is 1½", and 4-by posts are 3½".
• Width under 8": subtract ½". A 2x6 is 5½" wide.
• Width 8" and over: subtract ¾". A 2x10 is 9¼" wide.

What about length?

Good news: length isn't nominal. An 8-foot board is at least 8 feet long, and it's often a hair longer so you can square up the ends. The one exception you'll see is "precut studs," which are made shorter on purpose, at 92⅝" for standard 8-foot walls, so a wall frame comes out the right height once the top and bottom plates are added. If a plan calls for an 8-foot board, buy an 8-foot board, not a precut stud.

Plywood and hardwood sizes

Plywood

Plywood is sold in 4 x 8-foot sheets, and the sheet size is accurate. The thickness often isn't. Sheets labelled ¾" commonly measure 23/32", and ½" sheets commonly measure 15/32". That small difference matters when you're cutting a groove or dado for a shelf to slide into, so measure the actual sheet and size the cut to match.

Hardwood

Hardwoods like oak, maple and walnut use a different system, called quarters. Thickness is given in quarter inches of rough lumber: 4/4 ("four quarter") is about 1" rough, 8/4 is about 2". Once surfaced on both faces, 4/4 typically ends up around 13/16" and 8/4 around 1¾". Hardwood is also often sold in random widths and lengths, so you buy it by the board foot.

Mistakes this causes, and how to avoid them

1. Designing from nominal sizes. Two 2x4s side by side make a 3" wide leg, not 4". If you sketch your own project, always draw it with actual sizes.
2. Buying too little wood. Lumber is priced and counted in board feet using the nominal size, but your cuts use the actual size. Add 10–15% extra to every lumber list for mistakes, knots and warped boards. WoodBin's free Footulator board foot calculator makes the math easy.
3. Using plans that skip the hard parts. Vague plans that just say "use a 2x4 here" leave you to work out every measurement yourself. A good plan gives you a cut list: every board, its exact size, and where it goes.
4. Not checking boards for warp. Before you buy, sight down each board from one end. Leave behind boards that are bowed, twisted or cupped, and watch for big knots near the edges, which weaken the board.

Every RigalShop plan is built around standard lumber sizes you can find at any home improvement store, with a full materials list and a cut list for every board, so you don't have to translate a single measurement. If you're just getting started, our guide to the beginner woodworking tools you actually need covers what to buy before your first project.

Frequently asked questions