How to Measure and Mark With Precision





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.



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    I am sorry but I don't understand the "Step 4: Middle Marking and Finding Center" part... why I have to put the ruler diagonally? Thanks for this great instructable :-)

    2 replies

    Step 4 is easy, the reason you use Diagonally is because the ruler is equally marked out, so you just find two numbers, say the number 4 and 8, put those on the edges, and 6 is the middle point. You can use any numbers, just as long as you use 2 whole numbers to easily find the middle. The other example, the longer one, is if you want to section a board down to equal 1" sections, then you mark every inch between the two numbers. It took me a minute to think about why the ruler was being used this way and then I realized, it's not about the actual numbers, any 3 would work, just as long as you line up the two on the edge to give you the middle number; or what ever section you choose... I hope this helps...

    Step 4 makes it easier to divide or fine the center of the board you're cutting. Instead trying to find the middle of the board if it measures measures 7 1/2 inches across it's easier to place the ruler at an angle so that both ends of the tape measure is marked by an inch mark. So if you angled the ruler on the number 2" and the other end on the 8" then you'd know the middle of the board would be the 5"

    Lot's of clever ideas, thanks for sharing them...

    Very helpful! I never knew any of this! Thanks for sharing!

    So easy and yet so important. Great Instructtable. Awesome. Some I use, but two of them are so great. Thank you!

    Old school was to use a knife to make the marks, you can still see these in old furniture. The knife mark also helps to first make the cut, and on a circular saw it can help avoid chip out. That said I did learn from this instructable.

    More importantly, if striking a line against reference (measurement) marks, first place the point of the pencil on the reference mark, then incline it, move the straightedge to the inclined pencil point, then make the pencil line. This insures that the center of the pencil line actually aligns to the reference mark center. When I asked my first carpentry boss if he wanted me to cut to leave the line, or take the line - his response. "You take half and I'll take half!" This man measured twice, cut once - and you better d**n sure do the same! (BTW, in wood work we prefer a striking knife/scribe to a pencil when accuracy really counts!)

    I worked in an envelpoe making factory.We had over a dozen machines.English and German.made .After 15 years working on most of them,I decided to make the IS0 2000
    standard for the whole factory.The first thing I did was to buy a metal ruler That was tested and certified to be true..From there all the rulers I bought were tested against this one,and signed that I had tested.that way.. All our envelopes now are the right size.

    1 reply

    I have just made my 2nd Law ( Always check what I have written before I post to Instucts)

    ENVELOPE and NOT envelpoe. BUT then I know I:m not perfect. :-)

    Wow. I feel like a complete idiot. All these years of calculating the centre of boards. Just... wow.

    A man gave a presentation on measurement for woodworking. He made the point that the same ruler should be used throughout a project because they can and do vary from one another a little. I had never thought about that before.

    3 replies

    I heard from a colleague that he once compared folding meters at a building site. He found two - which were being used in construction - that differed by 4cm over 2 meters... So I completely agree.

    You think that's bad, I once bought a $500 paper cutter that was not square. I took it back and traded it for another, which also was not square! The third one was. That was back in college. Since then, I have boughten two drywall squares which were not square! It says "square" in the name, for God's sake!! lol

    what they need is....... GIANT CALIPERS

    Thanks for sharing these great tips
    And the photographs are simply amazing!
    How about an 'ible that share your secrets to photography ;)

    Great tips, I'll be putting them straight into practice.
    Thanks very much indeed :-)

    Thank you for sharing this. Really great tips! My favorite tip is the one for finding the center of a board without calculation.

    Favorited! Thanks for sharing.
    I'm the queen of "Measure twice, screws-up once".