Why use a Caliper?
Calipers are one of the quickest and most accurate methods for taking dimensional measurements. Most modern calipers can provide accuracy up to +/- 0.001 inches. The design of other handheld dimensional measuring devices, like rulers and tape measures, allow for a higher degree of uncertainty and human. Although their design has changed greatly, calipers have long been one of the preferred methods of dimensional measurements. In fact, the use of calipers as far back as the 6th century BC.
Before we explain how to use calipers, let’s first look at the major components of a caliper.
Measures the distance from an object’s edge to another point
Measures an object’s inner dimensions
When tightened, this screw holds the caliper jaws in place.
On most modern calipers, the blade displays both metric (top) and imperial (bottom) measurement.
Measures the outside dimensions of an object
Switches displayed units between metric and imperial
Sets the calipers current position to zero
Used to adjust the jaw’s position
Used to measure hole depth and thickness
- Step Gauge: Measures the distance from an object’s edge to another point
- Inside Jaw: Measures an object’s inner dimensions
- Locking Screw: When tightened, this screw holds the caliper jaws in place
- Blade/ Scale: On most modern calipers the blade displays both metric (top) and imperial (bottom) measurements
- Outside Jaw: Measures the outside dimensions of an object
- Inch/Millimeter Button: Switches displayed units between metric and imperial
- On/Zero Button: Sets the calipers current position to zero
- Thumbwheel: Used to position the jaws
- Depth Gauge: Used to measure hole depth and thickness
Caliper Setup & Inspection
Before using calipers, you must first perform an inspection then reset zero. Start your inspection with the calibration certificate. The certificate should show the maximum accuracy and display a next calibration date calibration. As we have previously covered, calibration is the only way to ensure accurate values.
If the calibration is up to date, it’s time to start the physical inspection. First, use the thumbwheel to gently open the jaws around 1/2 inch. This movement should be a smooth gliding motion with minimal resistance. Any resistance may mean you may need to loosen the locking screw or lubricate the blade. When everything is moving smoothly, inspect the measuring edges for debris and damage. If you are satisfied with their condition, close the jaws completely. Never force the jaws closed. A gap between the outer jaws could mean your caliper will require professional repair and calibration.
Once satisfied with your equipment’s condition, double-check that the jaws are closed completely, then zero the calipers. To set zero on dial caliper, rotate the bezel on the bottom of the dial until the dial points to zero. For digital calipers, press the on/zero button. Now you are ready to measure!
The 5 Primary Caliper Measurements
There are five primary types of measurements you can perform with a caliper, Inside, Outside, Depth, Step, and Compound. Below we will explain exactly what these measurements are and how to perform them.
Outside measurements are the most basic type of caliper measurement. These measurements can be used for measuring diameter, thickness, or the outside distance between two points. To make this measurement, simply open the outside jaws, place them around your object, then gently close the jaws until they make firm contact with your object. For an accurate measurement, assure the surface is parallel to the jaws. Never force the jaws closed around your object, as soon as there is resistance top your adjustment. If you over tighten the jaws, you run the risk of damaging your caliper and getting an incorrect measurement.
As the name implies, inside measurements can be used to measure the internal dimensions of an object. These are ideal for finding the diameter of a hole, or width of a channel/groove. To take this measurement, close the caliper jaws, and insert them into your object. Just like with the outside measurement, gently open the jaws until you encounter resistance. Since inside measurements can be a little more difficult to line up correctly, double-check that the caliper is making full contact with the intended surface and is not turned at a funny angle.
To make a depth measurement, set your object on a level surface and place the back end of your caliper on top. Make sure you leave enough clearance for the depth gauge is perpendicular to the surface being measured, and that it can descend completely to the level surface or the bottom of the hole. For the best results, we suggest the use of a surface plate as your level surface.
The ability to take a step measurement is an often overlooked feature available on many calipers. To make this measurement, open the caliper slightly and place the top caliper’s back edge, the sliding jaw, on the edge of your upper step. Next, lower the front edge, the fixed jaw, until it makes contact with your lower step. For an illustration, please see the diagram below.
The final type of caliper measurement is the compound measurement. This measurement either involves a combination of two or more of the measurements above and the zero button, for digital calipers or a little bit of math for dial calipers. Compound measurements are commonly used to find center distance, remaining thickness, and comparative measurements. To take a compound measurement, measure your first dimension, before removing the caliper from the object, hit the zero button. With your new zero, take your second measurement. The number that appears on the caliper is the difference between your two measurements. If you are using a dial or vernier caliper, you will have to write down and subtract the measurements to find your difference.