How to Use Calipers

Getting accurate measurements with different types of calipers

Co-authored by wikiHow Staff

Last Updated: October 9, 2022

Calipers are versatile for measuring straight objects less than 7.5 in (19 cm) long, the outer and inner diameter of round objects, or the depth of a hole.^{[1]
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Research source} Learn how to use calipers for performing experiments in physics labs, and use them properly to get accurate results.

Part 1

Part 1 of 2:

Taking Measurements with Vernier Calipers

1
Zero out the calipers before you take a measurement. Slide the clamps closed and push the extension rod in all the way to zero out Vernier calipers. Make sure that the measurement line is perfectly even with the zero.^{[2]
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- If the calipers are not properly zeroed before you begin, then your reading will likely be inaccurate.
Tip: Use Vernier calipers when you need the most precise measurements possible, such as for developing parts for a manufacturing operation or gathering data for a physics experiment. Vernier calipers are accurate to 1/20th of a millimeter!
2
Clamp the jaws around the outside of the object for external measurement. The calipers have 2 jaws that you can open and then close around the outside of an object. The outer jaws are located on the bottom of the measurement portion of the calipers. Open the calipers wider than the outside of the object and then close them around the part of the object you want to measure.^{[3]
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- For example, if you want to measure the outer diameter of a pipe, then open the calipers wider than the outside of the pipe and then close them around the outside of it.
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3
Extend the jaws inside of the object to get an internal measurement. Locate the inner measurement jaws on the top portion of the calipers (above the part that looks like a ruler). These jaws are smaller than the outer jaws of the calipers. If you need to find an object’s inner diameter, close the inner jaws of the calipers completely and put them into the object. Open the calipers until the inner measurement jaws are pressed against the inside of the object.
- For example, if you want to measure the inner diameter of a screw hole on a piece of furniture, then open the calipers until they are pressed against the inside of the hole to get your measurement.
4
Push the extension rod into the object for a depth measurement. Calipers can also measure the depth of an object or hole with an extension rod that you can pull out from the side (or end of the ruler section) of the calipers. Place the jaws of the calipers against the top edge of the object or hole, and then extend the bar down into the hole or object until it touches the bottom.^{[4]
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- For example, if you want to measure the depth of a screw hole, then place the caliper jaws against the rim of the hole and extend the bar down into the hole until you hit the bottom.
5
Record the measurement going from the largest to the smallest number. Record the numbers on the sliding scale going from the largest printed number to the smallest (top to bottom on the sliding scale). The first number will go in front of a decimal (even if it is a 0) followed by a decimal and then the other 3 numbers.^{[5]
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- For example, if the largest number is 4, then start by writing 4 in (10 cm).
- Next, if the next number is 1, then your new number would be 4.1 in (10 cm). Note that each mark between the second set of digits stands for 0.025 in (0.064 cm), so if the second number falls on the second notch between 3 and 4, then your new number would be 4.35 in (11.0 cm).
- Use the last digit to fill in the third space after the decimal. For example, if the notch is aligned with the 7 for this spot, then your final measurement would be 4.357 in (11.07 cm).
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Write whole number measurements with a decimal and 3 zeroes. Even if the number you get for your measurement is an even number with only zeros behind it, write it with 3 zeroes behind it. This will help to provide clarity for any calculations you perform with these measurements.^{[6]
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- For example, if your measurement for the inner diameter of a pipe is exactly 2 in (5.1 cm), record the measurement as 2.000 in (5.08 cm).

Part 2

Part 2 of 2:

Using Digital Calipers

1
Zero out the calipers before you get started. Slide the clamps closed and push the extension rod in all the way. Then, hit reset to display only zeros on the screen.^{[7]
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- Properly zeroed calipers are essential to getting an accurate measurement, so make sure to do this!
Tip: Opt for digital calipers when you need to get accurate measurements quickly, such as for replacing a part on an appliance or repairing a piece of furniture.
2
Clamp the jaws around the outside of the object for an external measurement. Calipers have 2 large jaws that you can open and close around the outside of an object. These jaws are located at the bottom of the ruler part of the calipers. Open the calipers so they are wider than the outside of the object, and then close the calipers around the part of the object you want to measure.^{[8]
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- For example, to measure the length of a nail, open the calipers wider than the length of the nail and close them so that 1 jaw is touching the head of the screw and the other is against the pointed end of the screw.
3
Open the jaws inside of an object to find the inner diameter. Find the inner measurement jaws on top of the calipers (above the part that looks like a ruler). These are smaller than the outer jaws. Close the inner jaws of the calipers and put them inside of the object. Open the calipers so the inner jaws are pressed against the inside of the object.
- For example, to measure the inner diameter of a pipe, open the calipers until they are pressed against the inside of the pipe to get your measurement.
4
Push the extension rod into the object for a depth measurement. Locate the extension rod on the side (or end of the ruler section) of the calipers. Position the calipers against the top edge of the object or hole, and then extend the bar down into the hole or object until it touches the bottom.^{[9]
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- For example, to measure the depth of a hole, place the caliper jaws against the rim of the hole and extend the bar down into the hole all the way to the bottom.
5
Look at the digital reading. Look at the screen and record the number. Keep in mind that the readout will include a zero or whole number followed by a decimal and 3 digits behind it.^{[10]
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- For example, the readout may say 0.365 in (0.93 cm) or 4.987 in (12.67 cm). Record the entire number as your measurement.
- Some digital calipers have a button to change the measurement from imperial to metric or vice versa. Check to see if this is a feature of your calipers and press the button if needed.

Community Q&A

Question

What are the sharp blades at the ends for? What can I use as a standard to check accuracy?

Community Answer

The tapered edges on each side help keep measurements of small parts accurate. Digital calipers allow you to reset zero at any position. You can set zero when closed, then measure against a ruler or any other measuring device.