How To Read A Tape Measure

How to read a tape measure

Learn the basics of tape measure use, or just brush up!

Building or renovating your home, hearth, and beyond is a task requiring accurate measurements using one of our most trustworthy & time tested tools: the tape measure. This guide will lay out how to use a tape measure and a few tips and tricks to make it easier.

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A note before we get started...

Most of the products that we sell are rigid and flat, and when measuring for precision it is important that you use steel tape measures and/or metal rulers and yard sticks. The best kind of tape measures have a locking mechanism that helps extend the tape slightly longer than the item to be measured, making the extended tape easier to handle.

You need to be certain that there is as little slack as possible in the tape when taking measurements. It is for this reason that using a non-rigid (cloth or plastic) tape is not desirable in almost all cases, as using one will lead to inaccurate measurements. The only time when using a cloth tape is acceptable is when measuring the circumference of something.

A rigid metal tape measure is usually desired when taking measurements.

If you can use this...

Metal Tape Measure

Don't use a cloth tape measure unless you are figuring out the circumference of something!

...then don't use this!

Cloth Tape Measure

You should also note that there is a style of tape measure called an "engineer's" tape measure that uses English feet but only has 10 units per foot instead of 12. This means that the "inches" on an engineer's tape measure are larger than a normal Imperial (English) inch. Just look at this example:

Types of Tape Measures

We don't use the decimal units when measuring and people have made the mistake of taking measurements with them and then ordering a custom product which didn't fit. Returns on many custom products are near-impossible, so please just make sure that your tape measure uses the standard Imperial (English) twelve inches per foot.

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So It's Not Everyday You Have to Read a Tape Measure...

So how do you measure effectively? First find an extendable steel tape that has a locking mechanism. The lock keeps the tape measure extended. The type of tape we need has 12 inches in a foot. These inches and feet are what we will use to measure for your home.

Graduated Tape MeasureThe Little Marks Add Up to An Inch...

Here we see the marks between 8 and 9 inches. This is the called a "graduated scale, which specifies fractions such as 1/2", 3/4", or 3/8". The marks divide the inch into parts of an inch. For example, the halfway mark divides the inch 2 times, into 2 halves. So we call this mark the 1/2" mark. Others divide it 4 times, into 4 quarters of an inch. We call these marks the 1/4", 1/2", and 3/4" marks. If we divide 8 times, we get eighths of an inch, and so on.

Fraction Tape MeasureAdd Your Fraction to the Nearest Inch...

Using our example, we are at the 8 inch mark. The measurement shown to the left would be 8 1/2 inches. Adding any one of those marks to 8 inches is like adding a fraction of an inch. DIY Tip: Remember, a foot is equal to 12 inches. If you hear people say a measurement such as "4 feet, 4 1/2 inches" it would be the same as saying "52 1/2 inches".

Here's a Helpful Guide of all Fractional Measurements:

Cheat Sheet Tape Measure

Decimal conversion

 Inch Sizes   Decimal 
1/16 0.0625
1/8 0.125
3/16 0.1875
1/4 0.25
5/16 0.3125
3/8 0.375
7/16 0.4375
1/2 0.5
9/16 0.5625
5/8 0.625
11/16 0.6875
3/4 0.75
13/16 0.8125
7/8 0.875
15/16 0.9375
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Try This Video Guide for Further Explanation:

Check out the quick video lesson below by expert Kyle Dye.

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Even More Tips & Tricks: Ways To Be Fast

How Do I Find Diameter or Radius of a Pipe, Line, Ring, or Fitting?

Diameter & radius both have to do with circles or cylinders. The diameter of a circle is the longest distance between 2 points in the circle, and always divides it exactly in half. The radius starts in the middle of the circle and ends at any edge of the circle. So, 2 radii make 1 diameter. It slices a circle in half into two equal parts. To find diameter, you make this slice with the edge of your tape measure.

Examples of products that use diameter measurements:

Fire pits, fire pit covers and screens, many fire pit tables, fire bowls, scupper bowls,fire pit burner rings, and chimney systems.

Pipe DiameterThe Diameter is measured from one edge to the next, the radius will be half of this.

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What is O.D and I.D in Regards to Diameter?

Inner vs. Outer DiameterO.D. stands for "Outer Diameter" and is the farthest reach of the circular material you are measuring. If we were measuring a doughnut, its O.D. would be where the outer crust ends. I.D. stands for "Inner Diameter" and it is the space between the material on the inside of your object. In our case, the hole of the doughnut would be its I.D.

So O.D. is the outermost layer/crust itself, I.D. is the space/hole in the middle of the material. To measure both of these, you use the diameter tactic above.

Some types of fireplaces and stoves use pipe with two walls. In cases of this the outer diameter (O.D.) refers to the diameter of the outer wall while the smaller pipe in the center is measured with an inner diameter (I.D.). For example, a double-walled direct vent pipe with an outer diameter of eight inches (8") and an inner diameter of five inches (5") would be labeled 5" x 8" pipe.

Examples of products that use O.D. and I.D. measurements:

Chimney systems (such as direct vent pipe), round fire pit tables, some pipe fittings and adapters, and the top measurements of round fire bowls and scupper bowls.

Diagram showing the inner diameter and outer diameter of a round piece of metal.


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How Do I Tell If Something is Perfectly Square, Rectangle? How Do I Find The Center?

No carpenter's square handy? A little known quick trick to finding square, or making something square, is to measure from corner to corner across the middle. Note this measurement. Now switch corners...other corner to other corner, across the middle, like making an X. If this second measurement if the same as the first, you have a square. If you need adjustments and are able to move the material, you can slide edges or pull corners together. This will true up the corner to corner measurements.


Measure from one corner to the opposite corner.

Square Example 1

In this example, the lower left corner to upper right corner measurement is 33".

If the other corner to the other corner is the same length, you are square.

Square Example 2

The lower right corner to the upper left corner is also 33", so this rectangle is square.


If your first measurement and second measurement don't match, then your rectangle or square isn't "square." Look at this example:


Measure from one corner to the opposite corner.

Square Example 3

In this example, the lower left corner to upper right corner measurement is 32".

Measure the other corner to the other corner. If they don't match, it isn't square.

Square Example 4

The lower right corner to upper left corner measurement is 34". Because this doesn't match our first measurement, this rectangle isn't square.


Perfect SquareWhen your corners are squared (with a 90° angle at all four corners), the corner-to-corner "X" that is made will be your center point.

Examples of products that need to be squared:

Fireplace doors, fireplace mantels, fireplaces that have cabinets, DIY fire pit housings, square and rectangular fire pits, and grill islands.

The center of the "X" will be the middle of your rectangle or square.

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What is The 3 - 4 - 5 Rule For Making Corners Square?

Learn to square a corner using the 3-4-5 rule.

The 3-4-5 Rule is an alternative method to making something square. Instead of relying on two corners, or a box, you can use just one.

Starting from one corner, make a mark 3" down.

Starting from the corner out, measure 3 inches (or feet) down one edge and make a mark.

Make a mark from the corner to 4" on the other side.

Starting from the same corner, measure 4 inches (or feet) down on the other edge, make a mark.

When the two marks are 5" apart, you have a perfect square.

Measure from one mark on one edge, to the other mark on the other edge. If this distance is 5, your corner is squared. Adjust the corner until this distance is exactly 5 inches.

Examples of products that can be squared using this method:    

Fireplace doors, fireplace mantels, fireplaces that have cabinets, DIY fire pit housings, and grill islands.

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How Do I Find The Center of a Circle or Make Something Perfectly Round?

To find the center of a circle you must have two or more diameters. No matter where they are, the diameters will meet in the center. To be sure, trace 3 to 5 diameters. This will show whether your circle is true. If all diameters intersect in a neat point, you know your circle is true and round.

With three identical diameters, you can determine where the center of a circle is.

In order to make a rough circle from a center point, you'll need to follow these steps:

Tie a string loosely around a nail.

Place a nail where you want the center of your circle to be. Tie a string LOOSELY around the nail.

Wrap the string around a pencil -- adjust it to the length of the radius of the circle you want.

Starting from the nail, use a measuring tape to measure out the radius (remember: a radius is half the length of the diameter) of the of the circle you want. Place a pencil at or marker at the length that you want. Wrap the other end of the string around your marking tool.

Holding the string tightly to the pencil, trace a circle around the nail.

Holding the string tightly to the pencil (or tape it if you would like), pull the rope taught and begin to drag the pencil around the circle. The loose knot in the center should move with your pencil. If it doesn't, you could end up with a spiral shape.

The result should be a perfect circle.

Once your circle is done, your diameter should be the same all the way around.

This method also works great on a larger scale for landscaping or other places you need large, perfect circles -- just swap the string and nail for a rope and stake.

Examples of products that benefit from tracing a circle:              

Firebowls, fire pits, DIY fire pits, fire tables, the base mounts of certain gas lamps, and scupper bowls.


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What If I Can't Measure Inside My Stove Pipe? What If It's Smashed?

How do you find the diameter of something you can't measure from the inside, or something that's crushed? We can use a bit of math and a piece of string. Better yet, a flexible fabric, surveyors, or sewing style tape will make it a bit easier.

In the following example, we'll be assuming that a cloth tape is unavailable, and so we're going to be using string to take the measurements. You should also have a rigid measuring tape handy to measure the length of the string with.

You can use a soft cloth tape for this type of measurement if you want!

Wrap a string around the round or dented surface you want to measure and mark where it crosses.

Use your string or fabric tape and measure around the outerside circle, or circumference. Hold the string against any dents for more accurate measurements.

Take the measurement at least two more times to be sure.

Check at least three places along the pipe's length, remember to hold the string as tight and flush against the pipe as you can.

Measure the length of each string to the mark. This example shows that it is most likely 12-9/16".

Using a rigid tape measure, measure each string. Assume that the majority of the measurements are accurate.

Convert the fractional measurement into decimal. In our example, 12-9/16" becomes 12.5625".

Convert the fractional measurement to decimal (see the conversion chart).

Divide the result by "pi." For simplicity, assume that pi = 3.14. Round the result to the nearest inch increment, in our example, that is 4".

Divide the decimal number by pi (for simplicity's sake, assume that pi is equal to 3.14). This new number is the diameter. Because some stove pipe commonly comes in 4" diameters, it is safe to round our measurement down to 4"



You can use these techniques to easily find the diameter of anything round.

Decimal conversion

 Inch Sizes   Decimal 
1/16 0.0625
1/8 0.125
3/16 0.1875
1/4 0.25
5/16 0.3125
3/8 0.375
7/16 0.4375
1/2 0.5
9/16 0.5625
5/8 0.625
11/16 0.6875
3/4 0.75
13/16 0.8125
7/8 0.875
15/16 0.9375


Examples of products that can be measured using the circumference:

Fire bowls, stove and chimney pipe, the exhausts of furnaces, stoves, and prefabricated fireplaces, and starter pipe.


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How Do I Measure Area, Surface Area, or Volume of a Box?


To find area, multiply the width times the depth.

If you can measure 2 sides of a surface, you can find its area. Most of the time this is known as either square inches (SQ IN or inch²) or square feet (SQ FT or foot²). To find the area of something that's already been "squared," measure its length and its width, then multiply them together.


To find the surface area of a box, find the three areas and multiply by two.

The surface area of a box can be calculated by measuring the width, depth, and height, finding the area by multiplying each pair of these surfaces together, then doubling it.

Put simply:

  1. Multiply the WIDTH by the DEPTH to get AREA A
  2. Multiply the WIDTH by the HEIGHT to get AREA B
  3. Multiply the HEIGHT by the DEPTH to get AREA C
  4. Add AREA A, AREA B, and AREA C together
  5. Multiply the number by two (2)

This will give you the total surface area.

You can find the surface area of any shape by adding the area of every surface together.

If you need to think about it in other terms, you can imagine the sides of the box separately (as in the exploded view above). You can use this technique to calculate the surface area of any rectangular surface, you just need the area of each surface to add together.

In this example, add AREA A1, AREA B1, AREA C1, AREA A2, AREA B2, and AREA C2 together to get the total surface area. Please note that all of these measurements should be in square inches (SQ IN) or square feet (SQ FT)

If you need to find more than one surface area, calculate them all, then add everything up. For example, the surface area of a piece of paper is 99 SQ IN. The surface area of a cube made from 6 pieces of paper would be 594 SQ IN.


To find the volume of a box, multiply the height by the width by the depth.

To calculate the volume of a box, all you need to know is the measurements of the width, height, and depth. Just multiply them together.

If you can measure three sides of the example paper box you just made, you can find its volume. Volume is the 3-dimensional space inside something and is known as either cubic inches (CU IN or inch³) or cubic feet (CU FT or foot³). First measure its length, then its width, then its depth. Multiply these three values together to find volume. Our paper box would have a volume of 891 IN CU.

Examples of products that frequently use area measurement:

Replacement stove and fireplace glass, mesh curtains, and hearth pads.

Examples of products that frequently use surface area measurement:

Stove and fireplace paint, grill islands, DIY fire pit enclosures, and outdoor fireplaces.

Examples of products that frequently use volume measurement:

Burner inserts, lava rock and fire glass, fire bowls and planters, and wood burning fireplaces, and stoves.


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What Are United Inches?


The united inch (UN) is easier to understand than area or volume, but doesn't seem to make as much sense. It's used as a way for suppliers to estimate total costs in a (very) general way. It also allows them to make a variety of odd sizes fit in a single price matrix.

Many hardware stores use united inches when tracking inventory. To find united inches, simply add the length and width of your surface. For example, a surface of 20 wide by 10 deep would have a UN of 30.

We will never ask you for measurements in UN.

To find the united inches, add the width and depth of your surface.

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How Do I Tell If Something is Level?

Use a bubble level. The goal is to make the bubble float nicely between the lines. You then know your surface is parallel to earth. Unfortunately a tape measure alone cannot do this - unless you are working from a surface you know is level (or a surface you want to be square to, even if it isn't). If you have a surface to work from, take three measurements across the span you need to be level and make marks. When mounting, line up to those marks, and check for square.


Box levels are great for checking flat surfaces.

Box levels include carpenter's levels, mason's levels, and torpedo levels. These levels are designed to set against straight flat surfaces. Most have at least two level angles to help make sure that both flat and 90° angles are level. You can usually get box levels as long as 72"

Line levels are used to check long distances for leveling.

Line levels clip to string that has been stretched taught between two posts, to determine if they are level. They're great for long distance leveling.

Circle levels are perfect for checking tables for leveling.

Circular levels are designed to set face-up on flat surfaces like table tops. Once the bubble is in the exact center of the circle, the surface is level.

Pitch finders or angle locators are great for measuring angles.

Angle locators (also called pitch levels) are used to measure the slopes of things that aren't necessarily supposed to be level, like roofs.

Using one or numerous levels for your projects can greatly enhance your stability, and modifications and replacements in the future.

Examples of products that need to be leveled:

Scupper bowls, grill islands, furnaces, stoves, and prefabricated fireplaces, fireplace mantels, and fireplace doors.

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How Do I Tell If Something is Parallel?

Highways with grass dividers are typically considered parallel.

To understand how to make something parallel, we need to understand something that IS parallel. Imagine an interstate highway with a grass divider between. We see these everywhere...and they are always parallel.

Parallel lines are equidistant from each other.

Parallel lines (like the top and bottom of a fireplace door) should be evenly spaced for their entire length.

Lines that will eventually intersect are NOT parallel.

Non-parallel lines will eventually intersect. Even if you can't see the slope with the naked eye, they will have different sizes between them that can be measured.

Perpendicular lines intersect at a 90° angle.

Perpendicular lines are lines that intersect at a 90° angle. This is what we mean by "squared" lines. The goal of almost every new installation and remodel is to get the lines square and level.

Examples of products that use parallel lines:

Fireplace doors, grill island componentsstoves, and fireplaces.

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How Do I Measure The Age of a Tree, Stump, or a Mantel's Wood?

The age-old secret is to count the rings. Look at the wood's end that is cut against the grain. Start from the center point and begin to count rings until you reach the furthest edge. If this edge is flat, you need to estimate the rest of the rings. Depending on the diameter of your log, try to guess how many more rings there would have been before it was sawn. The number of rings is the age of your wood when it was harvested.


Trees gain one ring for every year of growth.

Trees gain another ring of bark every growing season. There is one growing season per year.

This example has 29 rings, so the tree was 29 years old.

In this example, there are twenty-nine (29) rings, so this tree was 29 years old when it was cut down.


Examples of products that you can use this method on:

Log mantels

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How Do I Measure a Fireplace Door?

We thought you would never ask! We have a whole section built for fireplace doors, along with a stash of other info like how-to's, guides, and FAQ's for all that is hearth, home, & outdoor.

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Thank you for reading our measurement guidebook. We hope this helps everyone to master measurements tackle tape rulers.

Thanks for visiting!

-The CJ's® Team


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Do you have questions? Please call our friendly experts at 1-888-986-1535, start a live chat, or email us at [email protected].


Last updated on August 15th 2017.