Fact Checked

What are Outside Calipers?

Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

An outside caliper is a device which is used to measure the exterior diameter of an object, or to measure the thickness of an object. These tools can be tremendously useful in a wide range of settings, from archeology to zoology. They are available from scientific suppliers, some hardware stores, and other stores and companies which stock devices which can be used to take measurements. Specialty designs and designs with custom systems of measurement are available from some manufacturers by request.

The design of outside calipers consists of a pair of arms or jaws which curve inwards. People can extend the arms, and then tighten them around the object being measured. The inward curving points grip the object, and a reading can be taken from the calipers once it is clear that they are in position. By contrast, inside calipers designed to measure interior diameters have outward curving arms. Many different units of measurement are available with this measuring device.

An outside caliper.
An outside caliper.

One advantage to using a caliper for measurement is that the device is extremely precise. The points of the caliper allow the user to see precisely when the caliper is in position, and eliminate the need for eyeballing and guesswork, two common problems which arise when measuring three dimensional objects. These devices are also nondestructive, allowing people to take measurements without destroying or disturbing the object being measured, which can be important when working with rare or valuable objects. Outside calipers can measure anything from a delicate egg to a pipe used in plumbing.

The mechanism used to adjust and control the caliper depends on the design, with several options available. Spring and dial mechanisms are two common variations which are usually readily available. It is also possible to find locking devices which can be used to take and hold a measurement, which may be useful in various settings.

Like other measuring devices, outside calipers function best when they are cared for appropriately. It is important to make sure that the device is not bent or twisted, which can throw measurements off. It is also important to keep outside calipers clean and well oiled so that they will move smoothly, and to prevent the transfer of dirt or impurities between objects being measured. Outside calipers may sometimes come with a protective case which is designed to keep them in good condition, and it is a good idea to get in the habit of using the case when the device is not in use.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AboutMechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AboutMechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


I actually worked on a factory assembly line for a couple of years. The plant made interior lighting equipment, and part of my job was to do quality assurance checks on different parts that came off of the line. For one of the things, I had to use calipers to measure the diameter of a certain piece and make sure it was within certain limits. If they were being attached with too much of a gap, the rest of the pieces wouldn't fit into place correctly.

The thing I always thought was interesting was the accuracy of the calipers. When I first started the job, we were using analog calipers, so there was a dial on the calipers that gave the reading. Even then, you could get down to I believe a hundredth of an inch accuracy.

Soon after I started, they replaced the analog calipers with digital ones that had an LCD screen. They were even more accurate, getting down to a thousandth of an inch. Even though we didn't need that kind of accuracy, it was still impressive that something could be that precise with a measurement.


@kentuckycat - You're right that most of the uses for calipers are with the outside, but you can use the inside calipers any time you're trying to measure the interior or something. The most common use I can think of is for measuring the inside of a piece of tubing.

When I was a grad student, I used calipers a lot. Part of my research was the measure a bunch of tree seedlings. To measure the diameters of their stems, I had to use calipers. We had a couple of different types, but my favorites were the plastic calipers. They were fairly inexpensive, but moved a lot easier than the more precise, and expensive, metal ones we had. We also had a set of calipers that were waterproof.

As far as cost goes, I am not certain, but I think the waterproof set we had was around 100 dollars, so they aren't extremely expensive.


So, the thing I am sitting here wondering is, what would you use inside calipers for? I have seen calipers be used for plenty of things, but it has always been the outside kind.

Besides that, just because I am curious, where would you buy calipers? I am pretty sure I have never seen them in a store anywhere. I guess the normal person probably wouldn't have much use for them, so maybe you can only find them in special scientific catalogs. How much would a pair of calipers cost if you wanted them?


@MrsWinslow - I would say there are a few different reasons you could get different readings. The first thing I would think is that maybe you are going to a different mechanic who has a different set of calipers that are calibrated differently. Theoretically, you would think they should all be calibrated the same, but one place might not be doing it correctly.

Even if you are going to the same place, you might have a different person taking the measurement each time. In my experience using calipers, the amount of pressure you put on them can cause a pretty significant difference in the final reading.

I don't know what the brake caliper tool looks like, but if they are plastic calipers, they are even more susceptible to give more variable readings. My guess is that the measurements aren't too different from each other, so as long as none of the numbers are too low, I wouldn't worry about the differences.


@MissDaphne - Probably you're right that they would be the outside kind. The calipers *can* be a very accurate measurement, but it depends on the skill of the technician. Most people can get all the information they need about their body fat from their BMI (body mass index; a function of mass, basically weight, and height) with the addition of their waist circumference.

What I want to know is, if mechanics use a special brake caliper tool to measure how much brake you have left, why do I get a different answer every time I go in to have my brakes checked? According to the last guy I saw, my brakes actually got thicker between checks!


I've heard that calipers can also be used to measure a person's percentage of body fat. Would body fat calipers be outside calipers? It seems like they would have to be as they certainly aren't measuring anything *inside* your body!

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    • An outside caliper.
      By: Adem Demir
      An outside caliper.