How To Read Calipers

The tool, not the brake part.

byTony Markovich|
Maintenance & Repair photo


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Never forget this: There is a tool for everything. And not just a general mixed-use tool. There is a tool specifically designed for the job you’re doing. Take rulers, for example. They’re one of the oldest and most essential tools out there, but they still have their limitations and downsides.

A caliper tool, also referred to as a pair of calipers, is essentially a more advanced and niche version of a ruler. It measures parts in a specific way for specific jobs, specifically speaking. Because of this, they’re a bit more complicated than the straightforward nature of a ruler.

To better understand how to read calipers, it’s best to learn what they are and how they work. To assist you in that process, The Drive’s backyard editors have created a guide to the core basics of this unique tool. Let’s get started.

What Is a Caliper?

A caliper is a handheld device for precisely measuring the dimensions of relatively small items, not a part of your braking system. They come in a variety of styles and use different measurements, most often inches and millimeters. 

Types of Calipers

These are the most common types of calipers you will encounter.


Vernier calipers utilize two different scales, a main scale and an even more precise Vernier scale.


A dial caliper reads part of the dimension out on a small attached clock-like dial with a rotating hand.


A digital caliper reads the dimensions out on a small digital display screen. They typically also feature a few extra buttons. 

Calipers are typically made of metal., Depositphotos

Anatomy of a Caliper

To know how to use a caliper, you must know what each piece of the tool is for.

Lower Jaws

These claws are used to measure width, length, distance, or diameter of the outside of a part.

Upper Jaws

The upper jaws are used to measure the diameter of the inside of a part.

Locking Screw

The locking screw, often found near the upper jaws, locks the caliper in place.

Thumb Screw/Wheel

Slide the jaws open or closed with the thumb wheel. This screw also moves the depth gauge.

Main Scale

The primary graduated scale seen on the main stalk of the caliper.

Vernier Scale

The secondary sliding scale attached to the main scale.

Step Gauge

Used to measure the distance between an edge and another point on something.

Depth Gauge

Found at the tail of the caliper opposite the jaws is the depth gauge. The depth gauge can be used to measure something’s depth. 

On/Zero Button

On digital calipers, the button used to turn the device on and zero it out.

Inch/Millimeter Button

On digital calipers, the button used to switch the measurement between inches and millimeters.

ABS Button

The ABS button on a digital caliper will temporarily reset the reading to zero where the caliper lies.


The dial found on dial calipers displays the measurement reading using a rotating hand.

Digital Display

The digital screen on digital calipers shows the measurement reading in easy-to-read digital numbers.

Some calipers are digital., Depositphotos

The Basics of Reading a Caliper 

Estimated Time Needed: Less than 10 minutes

Skill Level: Beginner

Vehicle System: NA


Depending on how, what, and where you’re measuring, you might need proper safety gear. If you’re working on your vehicle, use these items at a minimum:

Everything You’ll Need To Read A Caliper

Just a caliper and something to measure!

Organizing your tools and gear so everything is easily reachable will save precious minutes waiting for your handy-dandy child or four-legged helper to bring you the sandpaper or blowtorch. (You won't need a blowtorch for this job. Please don’t have your kid hand you a blowtorch—Ed.)

Here’s How To Use A Caliper

Whether using a digital, dial, or Vernier caliper, they are all generally used in similar fashions. It might seem obvious, but here are the steps to follow:

Measuring Inside

  1. Unlock the top screw.
  2. Zero the caliper.
  3. Insert the upper jaws into the hole of the item you are measuring.
  4. Expand the jaws until they reach opposite sides of the hole.
  5. Lock the top screw.
  6. Take the measurement.

Measuring Outside

  1. Unlock the top screw
  2. Zero the caliper
  3. Open the lower jaws to be bigger than the item you are measuring.
  4. Tighten the jaws evenly around the item
  5. Lock the top screw
  6. Take the measurement.

Measuring Depth

  1. Position the caliper perpendicular to the top of the hole and parallel with the depth you are measuring.
  2. Unlock the top screw
  3. Zero the caliper
  4. Use the thumb screw to scroll the depth rod to the desired depth.
  5. Lock the top screw.
  6. Take the measurement.

How To Read a Dial Caliper

  1. Read the number on the main scale by looking at the last passed graduation mark next to the lower jaw.
  2. Read the number on the dial by looking at the number the hand points to.
  3. Add the two together to get your reading.

How To Read a Vernier Caliper

  1. Find the zero hash mark on the sliding lower scale and read the last passed graduation mark on the main scale.
  2. Now, pay attention to how the lines on the sliding vernier scale relate to the lines on the main scale. The way it is designed, only one of these lines will perfectly match up with each other. Find the line that matches. Note that number and its measurement from zero.
  3. Add the two together to get your reading.

Get Help On How To Read A Caliper From Mechanic On JustAnswers 

The Drive recognizes that while our How-To guides are detailed and easily followed, a rusty bolt, an engine component not in the correct position, or oil leaking everywhere can derail a project. That’s why we’ve partnered with JustAnswers, which connects you to certified mechanics around the globe, to get you through even the toughest jobs.

So if you have a question or are stuck, click here and talk to a mechanic near you. 

FAQs About Caliper Tools

You have the questions, The Drive has the answers.

Q: How Much Do Digital Calipers Cost?

A: A variety of calipers are available ranging in quality and cost between $20-200.

Q: Are Digital Calipers More Accurate Than Dial Calipers?

A: That depends on the caliper, but dial calipers do have an extra instrument that could be thrown out of calibration if not careful.

Q: What Are the Best Digital Calipers?


The Drive’s review team has selected our picks for the three best digital calipers.


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