Fractions and Decimals on an Inch Tape Measure

Video Transcript:
While fractions are commonly used in construction and furniture building, it is generally more common to use decimal parts of an inch in manufacturing. An example of a decimal part of an inch would be to use point five to represent one half inch, and point two five to represent one quarter inch.  Understanding how to convert one system to the other is a useful skill that will help you understand inch measurements a lot better. 

In today’s video, we’re going to take a look at how to use decimals with a tape measure. If you’ve ever needed to convert fractional inches into decimals, or if you’re working with a blueprint or set of plans that uses decimals instead of fractions, this video is for you. Let’s look at how to use decimals on a tape measure that’s graduated in sixteenths of an inch.

 If you aren’t sure how to read the tape measure, you might go watch our video on how to read a tape measure.  We won’t be covering that in this video.

On tape measures like this one the inches are divided into fractions. Each of those fractions can be expressed as a decimal.   Some of these you may already know.  For instance, one half can be written as point five.  Try entering it on a calculator: One…divided by…two…. Gives point five inches.  You probably already know that one quarter is equal to point two five. Practice solving some of these that you may with your calculator. That way you will know that you are doing it right.

Now let’s look a little closer.

One sixteenth of an inch is equal to 0.0625 inches. One divided by 16 equals point zero six two five. One eighth of an inch, equals point one two five inches. One divided by eight equals point one two five. One quarter of an inch  is equal to point two five inches. One divided by four equals point two five.

You can do this with any fraction that is on the tape measure.  If you know the fraction on the tape measure, you can just divide to get the decimal form. Three sixteenth, for example, is point one eight seven five.  

It is helpful to memorize some of the more common decimal equivalents of the tape measure, for example here are the eights of an inch:

One eighth of an inch is point one two five. Two eighths, is one quarter inch, which, of course, is point two five. Three eighths is point three seven five. Four eighths is a half or point five. Five eighths is point six two five, Six eighths is the same as three quarters or point seven five, and  Seven eighths is point eight seven five. Seven divided by eight is point eight seven five.

Now that we’ve covered converting fractions to decimals, let’s switch gears and look at how to go from decimals to fractions. This method is almost as straightforward once you know one simple trick. The trick is to find the smallest division on the tape measure.  On our tape, the smallest division is one sixteenth of an inch.  Now we will multiply our decimal by sixteen.  That will tell us the number of sixteenths that is closest to the decimal.

Here is an easy example:  point five times sixteen is equal to eight.  So the fraction would be eight sixteenths.  Eight sixteenths, of course, is a half inch.

To convert point two five to the closest fraction on our tape, we will multiply point two five by sixteen. This gives us four. So the fraction is four sixteenths.  Four sixteenths reduces to one quarter, or we could just count up four of the sixteenths on the tape.

Unfortunately, we cannot represent all decimal values using sixteenths of an inch.  Some decimals will fall in between marks on our tape measure.  

Stay with me now, because here is where things become a little trickier.  What if we had a decimal such as point three three three inches.  Where would that be on our tape?  If we use our trick and multiply our decimal by sixteen, we get five point three two eight.  What do we do with that?  

  The nearest fraction is five sixteenths.  We get that from the five.  But the exact point on the tape measure would be a little bit past the five sixteenths mark.  It would be about thirty two point eight percent of the way past the sixteenth mark, to be more accurate. 

Generally you only need to know if the measurement is closer to one mark or another.  Here is another example to show you what I mean.  Let’s think about the decimal point eight inches.  Let’s use our trick and multiply point eight by sixteen.  We get twelve point eight.  So the decimal would fall past the twelve sixteenths mark and it would be eighty percent of the way to the thirteen sixteenths mark.  So it would be more accurate to round up to thirteen sixteenths.

Let’s look at another one, and I’ll let you try some.  If we had a decimal like point two eight inches, we would multiply point two eight by sixteen. The answer would be four point four eight.  This is very close to point five. So the measurement would be between four sixteenths (or one quarter) and five sixteenths. 

Now you can try some examples of both methods.  First of all, what is the decimal equivalent of this fraction?    Take a few minutes to figure it out.  Pause the video and have a look.

The fraction is five sixteenths. Five divided by sixteen is point three one two five.  Let’s do another to be sure you’ve got it.  What is the decimal equivalent of this fraction?

The fraction is seven eighths, and seven divided by eight is point eight seven five. Remember that this is one of those that it is good to memorize if you use decimals a lot.

Now let’s try going in the other direction.

What fraction is closest to point six inches?  Point six times sixteen is equal to nine point six.  That means the decimal falls past the nine sixteenths mark and is closer to the ten sixteenths mark.  This would mean that the measurement was just less than five eighths.  It is very close to the halfway point.

Here is one last one to try to be sure you are getting these.  

A measurement is point two inches long.  What is the nearest fraction on our tape measure? We multiply point two by sixteen and we get three point two.  That is just past three sixteenths, and it would fall here on the tape.

Now, keep in mind that if your tape measure has more or fewer marks, you would use that number instead of sixteen. For example, this ruler only has eighths of an inch marked.  If I wanted to find point two on this ruler I would multiply point two by eight and get one point six. This would be between the one eighth and the next mark of one quarter. It would be here, near the middle, but a little closer to the one quarter mark.

The real key to understanding tape measures and rulers is to use them a lot. So be sure and get plenty of practice doing this.