How To Measure Diameter With A Tape Measure

by Joost Nusselder | Updated on:  March 16, 2022
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It’s pretty simple to determine an object’s length or height. You can accomplish it with the help of a ruler. But when it comes to determining the diameter of a hollow cylinder or circle it appears to be difficult somewhat. I am pretty sure that many of us have tried to measure the diameter with a simple ruler at least once in our lives. I have been in that scenario numerous times myself.
However, measuring the diameter of a hollow cylinder or circle is not as difficult as it looks. You can do that easily if you know the basic procedure for it. In this article, I’ll show you how to measure diameter with a tape measure. Continue reading this article if you don’t wish to be bothered by the question anymore.

What Is A Tape Measure

A tape measure or measuring tape is a lengthy, thinner, malleable strip of plastic, cloth, or metal having measurement units printed on it (such as inches, centimeters, or meters). It is made up of a variety of components, including case length, spring and brake, blade/tape, hook, connector hole, finger lock, and belt buckle. You can measure the length, height, width of an object using this tool. You can also use it to calculate the diameter of a circle.

Measure Diameter With A Tape Measure

Before we measure the diameter of a circle, we must first understand what a circle is and what exactly is a diameter. A circle is a curved line with all points at the same distance from the center. And the diameter is the distance between two points (a point on one side and a point on the other side) of the circle that passes through the center. As we know what a circle is and what its diameter is, now we are ready to measure the diameter of a circle with a tape measure. You must take specific procedures to accomplish this, which I will detail in this portion of the post.
  • Find the circle’s center.
  • Attach the tape to any point on the circle.
  • Calculate the circle’s radius.
  • Determine the circumference.
  • Calculate the diameter.

Step 1: Find The Circle’s Center

The first step is to locate the center of the hollow cylinder or circular object whose diameter you want to determine. You can easily find the center with a compass, so don’t be concerned.

Step 2: Attach The Tape To Any Point On The Circle

In this stage attach one end of the tape measure somewhere on the circle. Now drag the tape measure’s other end to a position on the other side of the circle. You must ensure that the straight line connecting two points (one end and the other end of the measuring tape) goes through the circle’s center. Now, using a color marker, mark these two points on the scale and take a reading. Note that you should keep your readings in a notepad.

Step 3: Calculate The Circle’s Radius

Now you have to measure the radius of the circle. The radius of a circle is the distance between the circle’s center and any point on it. It’s extremely simple to calculate and you can do that with the help of a measuring tame or a compass. Place one end of the measuring tape in the middle and the other end on any point of the curved line to do this. Take note of the number; it’s the radius of a circle or a hollow cylinder.

Step 4: Determine The Circumference

Now measure the circumference of the circle, which equals the length around the circle. In other terms, it’s the circle’s perimeter. To determine the perimeter of the circle you have to use a formula which is C = 2πr. Where r is the radius of the circle(r= radius) and π is a constant whose value is 3.1416(π=3.1416).

Step 5: Calculate The Diameter

We’ve gathered all of the information we’ll need to figure out the diameter of the circle. We’ll be able to figure out the diameter now. To do so, divide the circumference by 3.141592,( C = 2πr/3.1416) which is the value of pi.
Calculate diameter
For example, if you wish to find the diameter of a circle with a radius of r=4, the circumference of the circle will be C=2*3.1416*4=25.1322 ( using the formula C = 2πr). And the diameter of the circle will be D=(25.1328/3.1416)=8.

Frequently Asked Questions (FAQs)

Q: Is it possible to use a ruler to measure diameter?

Answer: Yes it is possible to measure the diameter of a circle using a ruler. In this situation, the calculations will be the same as before, but instead of using a measuring tape, you will need to use a ruler to take your measurements.

Q: What is the most effective instrument for measuring the diameter of a circle?

Answer: Respectively measuring tape, calipers and micrometers are the most effective instrument for measuring diameter.


A long time ago, the diameter measurement method was discovered. Despite a long period passed, calculating diameter is still useful in several fields, including mathematics, physics, geometry, astronomy, and more. And it won’t change in the future. So, don’t ignore the importance of buying a good-quality tape measure. You’ll find all the information you need about measuring a circle’s diameter in this article. Please scroll up to the article and read it without further delay, if you have not done so already.
Also read: how to read a tape measure in meters

I'm Joost Nusselder, the founder of Tools Doctor, content marketer, and dad. I love trying out new equipment, and together with my team I've been creating in-depth blog articles since 2016 to help loyal readers with tools & crafting tips.