How to Read Any Type of Caliper

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Plus, the types of measurements you can take with a caliper

Co-authored by Amy Bobinger, BA Reviewed by Grace Imson, MA

Last Updated: March 2, 2026 Fact Checked

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• Vernier Caliper
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• Dial Caliper
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• Digital Caliper
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• Measurements
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• Fixing a Zero Error
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• Video
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• Tips

|Show more |Show less

Calipers are measuring tools used to precisely determine the width of a gap or object. They’re much more accurate than a tape measure or ruler. We’re walking you through how to use the three main types of calipers: Vernier, which uses a simple sliding scale; dial, which has a slide and a dial; and digital, which displays the measurement on a screen. We’ll also show you how to take different readings with the caliper, so you’ll be measuring like a pro in no time!

How to Read a Vernier Caliper

1. Press the caliper jaws firmly against the item you’re measuring.
2. Turn the lock screw to keep the calipers from shifting.
3. Use the measurement from the fixed scale as the ones and tens place (e.g., 1.1).
4. Use the measurement from the sliding scale as the hundredths and thousandths place (e.g., .043).
5. Add the two measurements together for the final reading (e.g., 1.143).

Steps

Section 1 of 5:

Reading a Vernier Caliper

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1. 
   1
   Place the jaws securely against the object you’re measuring. Slide the scale to open or close the jaws. Close them securely against the sides of the object, but don’t squeeze too hard. Tighten the locking screw to keep the scale in place.

   • Hold the calipers parallel to the item you’re measuring. If you tilt them, you’ll get an inaccurate reading.
   • You’ll use the large, bottom jaws of the caliper for most measurements, but if you want more guidance, check out our section on using the caliper for different types of measurements.
   • If your caliper has a fine adjustment screw, you can use this to make more precise adjustments.
   • Before you start measuring with your caliper, it’s a good idea to check for a zero error to ensure the tool is properly calibrated.
2. 
   2
   Start by reading the value on the fixed scale. Once you have the caliper jaws in the right position, find the 0 on the left side of the smaller sliding scale. Then, compare that to the fixed scale that’s engraved into the body of the caliper. Find the nearest mark that’s touching or just to the left of that 0.

   • Most calipers have both an imperial and a metric fixed scale—use whichever you prefer.
   • If you’re measuring in imperial, the whole numbers are inches, and the hash marks between them are 1/10th of an inch. For example, if you’re measuring in inches and the 0 on the sliding scale is just past the third hash mark after the 1, your fixed scale reading would be 1.3 inches.
   • If you’re measuring in metric, the whole numbers represent 10mm and the small hash marks are 1mm. So if your 0 lines up with the second hash mark after the 2, your fixed scale reading would be 22mm.
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3. 
   3
   Check the sliding scale for additional digits. Carefully examine the sliding scale, starting at the 0 mark and moving right. Stop when you find a mark on the sliding scale that lines up exactly with the mark above it on the fixed scale. (Only one line on the sliding scale will perfectly match up.) The hash mark that lines up will give you the second part of your reading.

   • For instance, if the third hash mark after the 4 lines up with the fixed scale above it, your fixed scale reading is 4.3. If your sliding scale measures at a scale of 0.01, your fixed scale measurement is 0.043.
4. 
   4
   Add the two values together to get your final answer. This should be a simple case of writing the fixed scale digits, then writing the sliding scale digits afterward. Check the unit engraved on each scales just to make sure.

   • For example, your fixed scale measures 1.3 and is marked "inches." Your sliding scale measures 4.3 and is marked "0.01 inches," meaning it represents 0.043 inches. The exact measurement is 1.3 inches + 0.043 inches, or 1.343 inches.
   • If your caliper has a zero error, remember to subtract it from your measurement.
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Section 2 of 5:

Reading a Dial Caliper

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1. 
   1
   Calibrate the caliper, adjusting the dial if needed. Close the jaws completely. If the needle on the dial doesn't point to zero, rotate the dial with your fingers, until the zero is beneath the needle.

   • You may need to loosen a screw at the top or base of the dial face before you can do this. Tighten the screws again after you've made the adjustment.
2. 
   2
   Close the jaws around the object to take the measurement. Close the larger, flat jaws around an object to measure the outside diameter or width, or insert the smaller, curved jaws into an object and expand to measure the interior diameter or width.

   • You can also use the sliding stick at the end of the caliper to read the depth.
   • Close the locking screw to keep the calipers from sliding out of place while you take the measurement.
3. 
   3
   Write down the scale value. Look at the scale above the jaws of the caliper. Write down the measurement of the last hash mark you can see. (You may be able to see a number but not the hash mark beside it—don’t use this number or your reading will be inaccurate.)

   • For instance, if you’re measuring in centimeters and the fixed scale stops at the 5th line after the 5, your fixed scale reading is 5.5 centimeters.
   • Note: The inches scale of a caliper is typically an engineer's scale, with each inch divided into ten parts (0.1) or five parts (0.2). This is different from most rulers, which display 1/16ths or 1/8ths of an inch.
4. 
   4
   Write down the dial value. Look at the needle on the dial. The number it points to will give you your dial reading, which is an additional value for more precise measurement. The units should be labeled on the dial face, typically 0.01 or 0.001 cm or in.

   • For instance, if the needle on the dial points to 9.2 and the dial is labeled 0.001 cm, your dial reading is 0.0092 cm.
5. 
   5
   Add the two values together. Take your scale value and your dial value and add the two measurements. This will give you your final reading.

   • In our example above, the fixed scale displayed 5.5 cm and the dial reading was 0.092. Added together, your final measurement would be 5.5092 cm.
   • Unless you are working on a project that requires extreme precision, you can probably round this to 5.51 cm.
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Section 3 of 5:

Reading a Digital Caliper

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1. 
   1
   Zero the caliper before using it. Every time you use a digital caliper, you should zero it out first. Close the jaws of the caliper securely, without forcing them too tightly closed. Then, press the Zero, Tare or ABS button on the front of the caliper. This will ensure the tool is properly calibrated.

   • Most digital calipers will come on as soon as you open or close the jaws. If yours doesn’t, press the on/off button before zeroing it.
2. 
   2
   Close the jaws around the object you’re measuring. Use the larger bottom jaws to take an external measurement, like a diameter. Use the smaller jaws on top for internal measurements, like the inside of a pipe. Or open the jaws and use the slide tool on the bottom of the caliper to measure depth. Close the locking screw to keep the measurement from changing after you remove the object.

   • We’ll go over that more in our section on measurements you can take with a caliper.
3. 
   3
   Read the measurement on the screen. On a digital caliper, the measurement should be displayed on an electronic screen. There’s usually a button that you can use to switch between mm (millimeters) and inches (in).

   • Some calipers also have an option to display the measurement in fractions (F).
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Section 4 of 5:

Measurements You Can Take with a Caliper

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1. 
   Use a caliper to take internal, external, and depth measurements. Most calipers are designed to take three different types of measurements, depending on how you align the tool. Here’s how to take different measurements with a standard caliper:

   • Use the large clamps on the bottom of the caliper for external measurements, like the total diameter of a pipe from one outside edge to the other. Open the jaws wide enough to fit around the object, then close the jaws until the flat edges are flush against the sides of the item. Tighten the locking screw and read the measurement.
   • Use the smaller clamps on top of the caliper for internal dimensions, like the inside of a pipe. Slide the jaws inside the object you’re measuring, then open the jaws until the flat sides are flush against the inside of the item. Read the scale exactly like you would if you were measuring external depth.
   • Use the sliding stick on the end of the caliper to measure depth. When you slide the large jaws of the caliper open, a depth stick will slide out from the back of the tool. Insert this into the object you’re measuring, then read the scale on the caliper like you would for internal or external depth.

Section 5 of 5:

Correcting a Zero Error on a Vernier Caliper

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1. 
   1
   Compare the fixed and sliding scales to check for zero errors. Loosen the screw or screws holding the sliding scale in place. Move the sliding scale until the larger jaws of the caliper are fully pressed against each other. Compare the 0 positions on the sliding scale and the fixed scale, which is engraved on the caliper body.

   • If the two 0 marks are lined up exactly, there’s no error and you can use the caliper as-is. Otherwise, continue to the next step to correct the error.
2. 
   2
   Correct the zero error with an adjustment wheel if your Vernier caliper has one. While this is not common, some vernier calipers have an adjustment wheel on the sliding scale, which can be pushed to adjust the sliding scale without affecting the caliper jaws. If your model has this wheel, push it until the zeroes on the sliding scale and fixed scale line up, then take your measurement like normal. If it doesn’t, continue to the next step.

   • Watch the jaws closely to make sure you are not pushing a fine adjustment screw, which opens and closes the jaws by small amounts.
3. 
   3
   Subtract a positive zero error if the sliding scale is to the right of the fixed scale. If the sliding scale's 0 is to the right of the fixed scale's 0, read the measurement on the fixed scale that lines up with the sliding scale's 0. This is a positive zero error, so write this down with a + sign.

   • If the sliding scale's 0 is at 0.9mm on the fixed scale, write down "zero error: +0.9 mm."
   • For example, if your zero error is +0.9mm, and you take a measurement that reads 5.52mm, the actual value is 5.52 - 0.9 = 4.62mm.
4. 
   4
   Add a negative zero error if the sliding scale is to the left of the fixed scale. If the sliding scale's 0 is to the left of the fixed scale's 0, it’s a negative zero error. With the jaws closed, look for a mark on the sliding scale that lines up exactly with a value on the fixed scale. take the following steps:

   • For example, if the 6th mark on a 0.01 inch sliding scale is perfectly lined up with the line on the fixed scale, your zero error is -0.06 inches. Add 0.06 inches (or subtract -0.06 inches) to any reading to correct the zero error.
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Tips

• Periodically wipe down your calipers with rubbing alcohol or mineral spirits to remove dust and grime that can throw off the reading.
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