How to read a ruler

Answers to How to read a ruler

So you're trying to build a woodworking masterpiece and the plans call for you to cut a board to 4' 11-3/8". No problem….. Until you pick up the tape measure and realize that there is no clear marking for 11-3/8"!!! Now you need to understand how to read a ruler. It's actually a lot simpler than it looks.

The first thing we need to clarify is the symbols used in most woodworking plans. The symbol ' (apostrophe) represents feet. The " (quote) symbol represents inches. So a plan calling for a board to be cut to 4' 11-3/8" is asking for "four feet eleven and three eighths inches". Because this can be confusing most plans will call out this measurement only in inches; in this case 59-3/8" or "fifty nine and three eighths inches".

Now that we've covered the basics it's back to understanding all of those little marks on the ruler. A standard tape measure (or ruler) in the United States is divided up into feet and inches. Each foot is divided into 12 inches. The problem starts with the subdivision of the inches. In each inch there are a number of lines of different length. The longer the length of these lines, the larger the unit of measurement.

For example. 1. The longest line in the inch is in the middle. This is the half-inch mark and there is only one. 2. The next shortest line is the 1/4" (one quarter of an inch) inch mark and there are only two of these. 3. The third shortest line is the 1/8" (one eighth of an inch) mark and there are four of these. 4. The fourth shortest is the 1/16" (one sixteenth of an inch) mark and there are eight of these. 5. Some rulers will go a step further, down to 1/32" but this is often more precise that most woodworking cuts need to be.

On the typical ruler the basic (smallest) unit of measurement is 1/16". If you count the distance between two inch marks (one inch) you will find sixteen lines. This is because an inch is 16/16th of an inch long. Because we like to express fractional numbers in the largest unit possible we call it one inch. So it follows that if you have 8 lines, or 8/16" you have a half-inch or ½". And likewise, if you have 4 little lines, or 4/16" you have a quarter inch and so on.

At first it can be a little cumbersome to count these lines but over time you will learn to recognize the lengths and the different units of measurements they represent. This often starts with the ½" mark and progresses down the line. Over time a measurements like 59-3/8" can be located quickly.

You might have noticed that every 24" on the tape measure are marked with a contrasting black background and every 16" is marked with a red background. The marks are used by construction workers for spacing wood studs in a wall or joists in a floor/roof. 16" spacing is used most commonly for load bearing walls and 24" for non-load bearing walls. The small black diamonds represent a less common spacing scheme.

Terminology
A ruler used to be called a rule, and rulers would be rules. Today, the more commonly found term is ruler. The dictionary defines both the term rule and ruler, so either can be used, and for this document I will only use the term ruler.

Metric Rulers
Metric rulers are fairly easy to read. They deal with centimeters and millimeters only. You wont have to worry much about fractions.

Take a look at the following Metric Ruler.


The larger lines with numbers are centimeters, and the smallest lines are millimeters. Since millimeters are 1/10th of a centimeter, if you measure 7 marks after a centimeter, it is 1.7 centimeters long.

English Rulers
English rulers, are much more difficult to read. Mostly because they deal with fractions, which are a bit more dificult to learn.
Take a look at the following English Rulers.

A ruler marked in 8ths. Every mark is 1/8th of an inch.

A ruler marked in 16ths. Every mark is 1/16th of an inch.


The center mark between numbers is 1/2.

The red lines on these rulers are marked at 1/2, and 1.


The next smallest marks on a ruler are 1/4ths.


The red marks on these rulers are at 1/4, 1/2, 3/4, and 1. (1/2 is the same as 2/4)


The next smallest marks on a ruler are 1/8ths.


The red marks on these rulers are at 1/8, 1/4, 3/8, 1/2, 5/8, 3/4, 7/8, and 1.


The next smallest mark, if there are any, are 1/16ths.
The red marks on this ruler are at 1/16, 1/8, 3/16, 1/4, 5/16, 3/8, 7/16, 1/2, 9/16, 5/8, 11/16, 3/4, 13/16, 7/8, 15/16, and 1.

When marking down a distance from a ruler, mark the whole inch, followed by a space, then the fraction of an inch.

For example, 1 1/2, or 2 3/8.

When entering fractions into the conversion calculators, you have to seperate the whole number and the fraction with a + sign.

For example, 1+1/2, or 2+3/8.

Disclaimer - Answers to the questions are researched using various sources and are meant to increase the knowledge of our visitors. We cannot gurantee the accuracy of answers to questions.

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