How to Accurately Measure and Mark Lumber

Knowing how to measure and mark lumber is essential to all other carpentry skills. The success of many DIY projects will depend on accurate measurements and markings. Luckily, this doesn't require complicated or expensive equipment. You just need the correct tools and concentration.

For starters, if you don't already own a quality tape measure, buy one. Get one with a 25-foot-long blade that's 1-inch wide and has a lock to keep the blade extended, such as the Stanley PowerLock Tape Measure ($11, The Home Depot). The wide blade extends a long way without buckling. If possible, get a tape measure that doesn't have the first few inches divided into 32nds. These fine markings are rarely needed in carpentry projects and can be distracting. Learn to spot the 1/4- and 1/8-inch markings instinctively. They're good benchmarks for other measurements.

If you're a bit rusty, practice marking and cutting scrap pieces so you won't ruin an expensive piece of lumber. Be sure to take on-site measurements even if you've drawn precise plans ahead of time. Your plans might be perfect, but the work site might not be. What matters is that the boards fit where they're supposed to go, not whether they're cut to the precise size on your plan. Use our guide below to learn how to measure and mark lumber for successful DIY carpentry projects.

How to Measure Lumber

To make an outside measurement, hook the tape over the edge of one board and read the measurement at the outside edge of the other.

To take an inside measurement, push the hook against the inside edge of one board and read the measurement at the inside edge of the other. If necessary, you can bring the back of the tape measure case up to the opposite side of an inside measurement, then add the length of the case to the tape reading. This is less accurate, especially if the back of the case is not square.

Always keep the tape straight and at a right angle to the surfaces you're measuring. Tapes don't always agree, so your measurements might not match. Two tape measures, especially if made by different manufacturers, can vary by as much as 1/8 inch from one another. To keep all your measurements consistently accurate, always use one tape on a project.

How to Mark for Crosscuts

Crosscuts slice through a piece of lumber crosswise or perpendicular to the wood grain, allowing you to adjust the board's length.

Step 1: Check for square and mark.

Before cutting a board, make sure the end that you won't cut is square. If it's not, cut it square and remeasure. Hook the tape measure on the end of the board and extend the tape until you reach the length for the crosscut. Mark the measurement with a V, not a straight line.

Step 2: Mark the waste side.

Hold the pencil tip on the point of the V, and slide a layout square over until it touches the pencil tip. Mark a straight line to indicate when you'll cut. Draw a large X to signify the waste side of the cut.

How to Mark Rip Cuts

Rip cuts follow the same direction as the wood grain and are used to cut lumber by width. Because they run along the length of the board, rip cuts are typically longer than crosscuts and require very precise measurements and markings.

Step 1: Snap chalk line.

Mark the width of the cut on both ends with a tape measure or square. Hook a chalk line tightly on the marks and snap the line.

Step 2: Mark the length of the board.

If the cut runs parallel to the edge of the board, scribe a line by holding a pencil against a square at the proper width. Draw the square and pencil down the length of the board to mark the cut line.

How to Mark Miter Cuts

Miter cuts are angled crosscuts, which most often measure 45 degrees. For a 45-degree cut, measure to the long end of the miter, and set your combination square or layout square on the mark. Draw the cut line.

How to Use a T-Bevel

A sliding bevel gauge, also called a T-bevel, is a tool used to mark angles other than 90 and 45 degrees. It features a swinging blade that can be adjusted to any angle and tightened in place for tracing. To mark lumber using a T-bevel, set the blade and handle on the inside or outside edges of the boards and lock the blade. Then move the tool to the piece you want to cut, and mark the line along the blade.

How to Measure Lumber On-Site

Mark actual length measurements on-site whenever possible. No matter how accurately you take measurements with a tape measure, there's no substitute for on-site measurements. Any number of factors can throw a measurement off, and even a small discrepancy can make a difference. Remember that lumber dimensions might not be exact. For example, the actual dimension could be off by 1/32 inch, which your tape might not show, or you could forget which side of a marked line to cut. Position the stock with the cut end as close to the edge as possible without slipping off, and mark the cut line with a carpenter's pencil.