A Beginner’s Guide to Calipers – Dial and Digital

tesa dial caliper

A caliper is a measuring tool commonly used to check precise measurements in a variety of applications. The biggest strength of calipers is in their versatility. Calipers come in many forms, including digital, dial and vernier. They are commonly used to take measurements to an accuracy of .001″ or .01mm. Metric measurements can be made down to .01mm or .001mm.

Below is a list of the most common caliper uses:

  • Inside measurements – hole sizes, slot widths
  • Outside measurements – lengths, widths, diameters, thicknesses
  • Depth measurements – depth of holes, slots, step locations

How to use a caliper

Before using your caliper, check to make sure that the measuring tool and surface to be measured are free of dirt, debris, chips, etc. The body of the caliper should slide freely along the scale or bar. For an outside measurement, slide the jaws of the caliper open until they are far enough apart to be placed over the part to be measured. Now proceed to close the jaws while trying to keep the jaws perpendicular to the surface being measured. Multiple measurements should be taken to verify that the caliper has yielded the true reading. For example, if a measurement is taken where the jaws of the caliper are not perpendicular to the surface being measured then the reading obtained can be larger than the true size.

Note: Do not exert a large amount of force on the caliper in the direction of measurement. This can cause the tool to flex and distort the true measurement. It is best to place the same amount of force that is used to zero the caliper.

How to zero a digital caliper

To zero a digital caliper, close the jaws and check the reading of the caliper. If it reads all zeros great, you can stop here. Don’t be fooled into thinking that means your caliper is accurate, but it’s a start. For more info please see the how to calibrate your caliper below. If your caliper does not read all zeros then while in the close position press the zero or origin button. This button may have a different name based on the manufacturer of your caliper. If you are unsure of the proper button to use then check the manufacturer’s website. 

How to zero a dial caliper

To zero a dial caliper, close the jaws and check the reading of the caliper. If it reads all zeros great, you can stop here. Don’t be fooled into thinking that means your caliper is accurate, but it’s a start. For more info please see the how to calibrate your caliper below. If your caliper does not read all zeros then while in the close position, loosen the bezel screw nut. Spin the bezel until the caliper reads zero. Now tighten the bezel screw nut. Verify that the caliper still reads zero after tightening the screw.

How to read digital caliper

Reading a digital caliper is easy. The digital readout display clearly shows the measurement value obtained. Digital calipers are far superior to dial and vernier calipers in this regard. Digital calipers have the ability to quickly switch between metric and inch readings with fractional measurements available on some but not all digital calipers. The biggest downfall of this is the ease at which the zero setting can be changed on a digital caliper. Because of this it is best to check your zero setting at minimum each time you use the tool and if you are making a multitude of measurement, check the digital caliper occasionally during use.

If you need more help understanding the reading, see our article on Understanding Machine Shop Numbers & Values

How to read a dial caliper

Reading a dial caliper is easy, though not as easy as a digital caliper. Because costs have come down substantially in recent years, I recommend purchasing a digital caliper if possible. If a digital caliper isn’t in the cards either because of budget or because you are working with an inherited tool then keep reading. Dial calipers come in multiple varieties but most have their measurement read in the same way. Dial calipers usually have graduations along the bar that are in increments of .100″ or one hundred thousandths of an inch. Often the 1,2,3, etc whole inch increments are marked with a number and the .100″ increments will be marked with a line. To read the caliper combine all the visible whole inch and .100″ increments on the bar with the dial reading. Example: if you can see the 2 and 3 of the .100″ lines and have a reading on the dial of 46 then your caliper reading would be 2.346″.

If you need more help understanding the reading, see our article on Understanding Machine Shop Numbers & Values

Uses for a caliper

Calipers have multiple uses. They are commonly used to verify measurements in machine shops all over the world for a variety of products. Calipers are also utilized by home mechanics and businesses alike to perform specific tasks such as critical engine measurements. Calipers are a great all around measuring tool. More than any other precision measuring tool, they are capable of performing measurements on a large variety of parts. They have a larger measuring range when compared to micrometers and indicators. They are quicker to perform measurements when compared to micrometers or indicators. Go/no go gages are the only measuring tool that can take measurements faster but go/no go gages are very specialized.

What makes a good caliper

Whether digital, dial or vernier, a good digital caliper needs two things: precision and accuracy. Some adjustments can be made with most calipers to account for small errors in accuracy but nothing can be done to fix a tool that isn’t precise. A quality caliper will move smoothly without any drag. This is the telltale sign of a good tool. If your caliper ever feels like it is rubbing or dragging then it is most likely the result of damage from being dropped or contamination exposure. Unfortunately if you caliper isn’t moving smoothly there isn’t usually much that can be done besides oiling the tool and sliding back and worth. Then wipe off the oil and repeat the process over again. Make sure to consult the manufacturer’s instructions before performing this operation as calipers can vary and only use machine tool oil such as this one by Starrett.

Where to buy calipers

Calipers are available from a number of online retailers. For a more in depth guide of which calipers are best for your situation, please see our reviews section. Some general advice, as usual for most products Amazon has a number of good options available. Harbor Freight has a couple good options that are reasonably priced and well reviewed. Home Depot and Walmart both sell calipers but we do not recommend any that they currently offer. 

Are cheaper calipers as good as expensive ones?

While some of the cheaper (made in China) type calipers have gotten much better than they were in years past, they are nowhere near the same quality that you will see in a tool from one of the tried and true manufacturers such as Starrett or Mitutoyo. A caliper is the type of tool that is best to purchase once. In most cases it can be more beneficial to search for a used option on Craigslist or Facebook marketplace. For more information on the best calipers to buy for your application see our Best Calipers article.

How to calibrate a 0-6" caliper

  1. Verify that the caliper is clean.
  2.  Visually examine the caliper for any condition that could cause errors in the calibration.
  3. Close the caliper by sliding the body of the caliper until the outside jaws are closed.
  4. Hold the caliper to a light source and visually examine for light showing between the jaws. If the jaws are not parallel, light will show between them.
  5. Check accuracy of outside jaws of the caliper at various locations within the tool’s measuring range. Gage blocks which have been calibrated themselves should be used for this operation.
  6. Check the accuracy of the inside jaws of the caliper at various locations over the measuring range. This can be done by locking a micrometer that is calibrated at a know location and checking the gap.
  7. Check the accuracy of the depth rod (if applicable) using gage blocks to set the caliper on and extending the depth rod down to the surface plate.
  8. Adjustments can be made at this step as needed. Different calipers have different procedures for adjustment. Consult manufacturer documentation for instructions regarding the adjustment of your caliper if needed.
    1. Dial calipers are most often adjusted in the zero position by loosening the dial lock and spinning the dial until the tool reads zero.
    2. Digital calipers are most often adjusted in the zero position by pressing the zero or origin button. This button can vary between manufacturers so check your instruction manual if you have one. If not, don’t worry it is usually very easy to figure out what button zeroes the caliper.
  9. After adjustments are made, the tool should be checked again to verify the adjustment worked.
  10. Calibration results are commonly recorded in a register or database for traceability of measurement history

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