A Centering Rule





Introduction: A Centering Rule

About: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my first ...

I wanted a centering rule, and decided to make one from an 18 inch steel rule I own.


  • P-Touch Label Maker
  • Scissors
  • Knife


  • Steel ruler
  • Black on White label tape
  • White on Black label tape
  • Clear packing tape

Step 1: Make Numerals

I am alternating black on white numerals with white on black in order to lessen confusion when using the centering rule. I am making odd number numerals black on white. I am making even number numerals white on black. I left three spaces between each numeral when setting up the label maker. Because it is a centering rule, two of each numeral will be needed, one for the left side and one for the right side of center.

Note: If you do not have a label maker, you can write numerals on a strip of paper with a marker pen and tape or glue the paper strip to the ruler, perhaps even mark them on the ruler itself. You could even print the numerals on a computer.

Step 2: Apply the Numerals

I used a knife point to position the numerals before pressing on each to adhere them to the rule. (You might want to clean the rule of any oils from your skin before applying the numerals.)

This label tape has a slit in the backing paper that runs lengthwise. Simply fold the top half on the printed side toward the bottom half and the backing paper begins to separate. Lift off whichever half you wish. I lifted off the top half and attached the numeral to the knife tip.

Notice that I cut a triangular pointer from some of the scrap tape and applied it at the mid-point of the rule for zero.

Step 3: Remove the Other Half of the Backing Paper

Once the top of each numeral adheres to the rule, flex the numeral in place so the bottom half of the backing paper peels away from the numeral. Remove what is left of the backing paper.

Step 4: Cover With a Protective Layer

I want to protect the numerals from coming off later. In addition the markings on the rule are painted rather than inscribed. I stretched a strip of clear cellophane packing tape over the length of the rule and applied it so there are no trapped air bubbles. Then I used a knife to trim the tape flush with the edges of the rule. As it is, I can continue to use the rule to measure lengths up to 18 inches, or I can use it to find the center of something.

The photo in the Introduction shows the rule in use. You can see the center of the envelope is 2 7/16 inch from either side.



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    21 Discussions

    Great ible, I never knew of a centering ruler.

    This would have saved me some badly cut lumber due to mental errors.

    1 reply

    Thanks. I do not remember ever seeing one until I saw my son-in-law use one. I find it makes the job easier and less prone to the errors you mention. The purchased variety can be a little expensive, especially compared to the cost of an ordinary ruler you can turn into a centering ruler.

    I hope you don't mind me pointing this out, but a vast majority of Instructables could be purchased, isn't this the whole point of this site/community?

    BTW, fantastically simple, yet effective i'ble here Phil. This is one i shall use myself.

    Thank you, Alexandra. As for an Instructable showing how to make something one could buy, there have been times when I needed something, but did not feel I could spare the money to buy it. There are certainly others in that situation right now. Another great thing about Instructables is a project someone else shares may give me the inspiration to adapt part of that project to do something no one has done before.

    My thoughts exactly Phil. If ever I need to buy something, I always check here first to see if there is a cheaper alternative, plus I'm always one to recycle/upcycle before handing my hard earned cash over to big companies.

    Yes, you can. I have not seen them locally, but have seen them on Amazon. Shipping charges apply in addition to the purchase price. Making one from a ruler I already have was a very good solution for me.

    Thank you. I thought about it over several months before I finally came to what I would do.

    I've been meaning to order a centering ruler from Amazon. Glad I haven't. Once again, you've saved me a few bucks with a "why didn't I think of that?" solution, Phil. Thanks!

    2 replies

    I guess I haven't had much to say lately. Just reading 'ibles but not commenting. I do appreciate the effort you and all the others put forth.

    Thank you. I had thought a long while about how I could join two rulers end to end. But, there is a possible problem. Measuring devices may be made to read in the same units, but may vary a little over a dozen or so of those units. Then it came to me that I could use one ruler and add another set of numerals. Using one ruler eliminates the problem of a second ruler that may not read quite the same as the first. We will need to talk about the "brilliant" part.

    A MUCH easier way to find the middle of a page is to lay your ruler diagonally across the page with 1" on one side of the page and 11" on the other side The 6" mark will be center. VERY SIMPLE

    1 reply

    Thank you for your interesting idea. Soon I will use this centering ruler to measure an open space for two spacers to position a pulley midway between two mounts for an axle. There is no rectangle involved, but this centering ruler will tell me exactly how long each spacer needs to be. I can think of many similar applications where this is the right tool for the job.


    2 years ago

    This a great idea to make projects just a little bit simpler. Thanks fore the idea.