Introduction: How to Measure and Mark With Precision

About: The official instructable for Popular Mechanics magazine, reporting on the DIY world since 1902.

Measuring is the first step in wood-working. The second step is to make a mark on the measured point. The combination of the two processes—measuring and marking—forms the foundation of accurate work. If either is done incorrectly, much effort and material are wasted. Here are a few pointers that can improve the quality of your work by reducing the chance for error.

This project was originally published in the January 2001 issue of Popular Mechanics.  You can find more great projects at Popular Mechanics DIY Central.

Step 1: Ruler Selection & Marking

A wood folding ruler, a tape measure and a few steel bench rulers (6 in., 12 in. and 24 in.) meet most measuring needs (Photo 1). To mark from any one of these rulers, use a sharp 2H pencil, the best general marking device for woodworking. These pencils have a medium-hard lead and when properly sharpened leave a fine line that’s readily visible on most surfaces. When marking a line with a ruler, be sure to hold the pencil at an angle so that its point meets the workpiece at the same place the ruler does (Photo 2, left pencil). Holding the pencil perpendicular to the work surface results in the center of the pencil point being inaccurately positioned.

Step 2: Basic Measurement

When measuring from the edge of a workpiece, hold a stopblock next to the edge, then press the ruler against the block (Photo 1). For utmost precision, hold the ruler on its edge against the work surface (Photo 2). This way, the ruler’s markings meet the workpiece surface and you avoid mismarking the workpiece due to an off-center line-of-sight created by the ruler’s thickness. A similar distortion occurs when transferring the measurement from a tape measure. To avoid this, hook the tape’s end clip firmly to the edge of the workpiece, then tip the blade so its edge curves down to meet the surface. Then mark the dimension on the workpiece (Photo 3). 

Step 3: Measuring Circles

Use a pair of blocks and a ruler of sufficient length when measuring the outside diameter of a circular workpiece. Read the measurement at the inside edges of the blocks.

Step 4: Middle Marking and Finding Center

Dividing a board into any number of equal spaces can be done easily without calculation. Simply set a ruler diagonally across the board with the desired number of inch graduations divided between the board’s edges. Then make a mark at each graduation (Photo 1).

A similar method is used to find the board’s center. Angle a ruler across the board’s width so that a whole number on the ruler is at each edge of the workpiece. Find the midway point between the two numbers, and mark there (Photo 2). With either method, it doesn’t matter if you place the end of the ruler at the board’s edge or if you use the middle of the ruler.

Step 5:

To take the inside measurement of an assembly, use a folding ruler with a sliding extension. Hold the ruler against one end of the assembly, and slide its brass extension so that it butts against the other end of the assembly (Photo 1). The measurement of the sliding extension, added to the ruler’s dimension, equals the inside dimension of the assembly. Without a folding ruler, use a wood block and a ruler that is shorter than the interior dimension. Overlap the ruler and block, then add the block’s dimension to the dimension at which it overlaps the ruler (Photo 2).

Step 6: The Penny Trick

A last tip: you can use a penny to mark a 3⁄8-in. radius. Hold the penny as shown above and mark along its edge.