Reading the Micrometer

The micrometer is a device used to measure small linear dimensions, and is shown below. It is similar in some respects to the vernier caliper, but there are some important differences.

There is a fixed main scale on the barrel, which has a horizontal line down its length. The graduations above this line are full mm, while those below are half mm (you will see why this is so shortly). A sleeve rotates around the barrel, and is graduated at 0.01mm. The barrel and sleeve measurements are added to obtain the final measurement.

Start on the barrel. See how many full mm are visible, and whether or not the half mm is visible. Here, there are 8 full mm visible, along with the half mm, so start with 8.5mm.

Next, see where the horizontal line on the barrel hits the sleeve. Each of the graduations on the sleeve is 0.01mm, so starting at 0, they are 0.01mm, 0.02mm, 0.03mm 0.04mm, 0.05mm, 0.06mm, 0.07mm, 0.08mm, 0.09mm, 0.10mm, 0.11mm, 0.12mm, ... , 0.44mm, 0.45mm, 0.46mm, 0.47mm, 0.48mm, and 0.49mm - for a total of 50. [This is why you need the half mm on the barrel - every rotation of the sleeve only advances it along the barrel (50)(0.01mm) = 0.5mm] Here, the line hits between 0.07mm and 0.08mm, so add 0.07mm to the 8.5mm for 8.57mm.

Finally, as mentioned above, the horizontal line hit the sleeve between 0.07mm and 0.08mm, so you will need to estimate a final digit, which is to 0.001mm. Here, you are almost to 0.08mm, so 0.009mm is good. The final measurement is then 8.579mm (0.8579cm).

Virtual Micrometer Simulator

Example

(3)(1mm) + (36)(0.01mm) + (2)(0.001mm) = 3mm + 0.36mm + 0.002mm = 3.362mm (0.3362cm). 

Example

(10)(1mm) + 0.5mm + (20)(0.01mm) + (0)(0.001mm) = 10mm + 0.5mm + 0.20mm + 0.000mm = 10.700mm (1.0700cm).

Even though (0)(0.001mm) = 0, this final digit is significant, and needs to be recorded. Look at it this way - the measurement is neither 10.699mm nor 10.701mm - it is 10.700mm.

Example

(12)(1mm) + (48)(0.01mm) + (7)(0.001mm) = 12mm + 0.48mm + 0.007mm = 12.487mm (1.2487cm).

Be careful! Although you are beginning to see the half mm between 12 and 13, it is because you are almost there; i.e., it is not added in the measurement. If you advance the sleeve to 0 (one and a half graduations) - are you at 13mm? No - you are at 12.5mm.