What’s the difference between calipers and micrometers

Calipers are precision instruments used to measure physical dimensions, often inside measurements, outside measurements, or depths.

Micrometers are similar, but are often configured for more specific measurement types, such as only measuring outside dimensions or only inside dimensions. Micrometer jaws are often specialized.

For instance, these are inside micrometers, meant for measuring the distance between two points. Outside micrometers measure the thickness or width of an object, while inside micrometers typically measure the space between two points. These inside micrometers might be used for measuring the width of a hole or slot, for example.

What are the differences?
Following are some generalizations that I’ve found to be true over the years. There might be other differences, or some of these differences might not apply to all applications.

Accuracy
To start, micrometers are often more accurate.
My Mitutoyo 6″ digital calipers, for example, are accurate to ±0.001″, and with 0.0005″ resolution. My Mitutoyo digital micrometers are accurate to ±0.00005″, and with 0.00005″ resolution. That’s a difference of ±1/1,000 of an inch accuracy compared to ±1/20,000 of an inch.
What this means is that a caliper measurement of 0.500″ could be considered to be within 0.499″ and 0.501″, and a micrometer measurement of 0.50000″ could be considered to be between 0.49995″ and 0.50005″, if there are no other errors or uncertainties.

Ease of Use
Calipers are generally easier to use. Micrometers, on the other hand, require more finesse. If you’re not careful with micrometers, measuring the same thing 5 different times could result in 5 different measurements.
There are different types of thimbles, such as plain, friction, and ratcheting, that help with repeatability and the “feel” of taking measurements.
In high precision work, even the temperature of micrometers can influence measured values in a small way. That’s why some micrometers have insulated pads, to help reduce heat transfer from the user’s hands. There are also micrometer stands.
Micrometers, despite requiring more finesse, can be easier to use for measuring certain things, due to the smaller size of their jaws compared to calipers’.

Functionality
With calipers, you can use the jaws for light marking tasks. Doing so can wear or blunt the jaws over time, and so it’s not necessarily something you want to do, but it’s something you can do. Micrometers can only be used for taking measurements. And, as mentioned, calipers can often be used to make different kinds of measurements (inner dimensions, outer dimensions, depths), while micrometers are usually singular-task tools.

Specialization
Calipers and micrometers are both available with different styles and shapes of jaws. Ball micrometers, for example, are often used to measure the thickness of curved parts, such as pipe walls.
There’s something called offset centerline calipers, for example, with specially tapered jaws for measuring the center-to-center distances between holes. You can also find attachments for use with standard caliper jaws.
There are many different styles of calipers and micrometers, as well as some attachments, should your needs require them.

Size Range
Calipers often have a wide measurement range, such as 0-6″. Calipers are available in other sizes as well, such as 0-4″, and 0-12″. Micrometer measurement ranges are a lot smaller, such as 0-1″. If you want to cover the entire range between 0 to 6″, you need a 0 to 6″ set, which comes with 0-1″, 1″-2″, 2″-3″, 3″-4″, 4″-5″, and 5″-6″ sizes.

Use in Other Equipment
You can find caliper-type and micrometer-type gauges in other equipment. A digital caliper-like scale might serve as a height gauge for a planer, drill press, or mill, and a micrometer-like scale might be found in the stage adjustment of a microscope or other inspection tool.

When to use one over the other?
Do you need to make quick measurements? Or is higher accuracy more important? Are you measuring objects of widely different sizes?
Calipers are good to start with, especially if you’ve been using a ruler or tape measure for all your measurements. Micrometers are more of a “you’ll know if you need it” kind of tool.