Resolution is the step of the display. Accuracy is how close the reading is to reality. A digital caliper showing 0.01 mm has 0.01 mm resolution, and its accuracy is usually stated separately at ± 0.02 mm — twice as coarse.
Why both numbers exist
A display has to round to something. That rounding step is the resolution, and it is a design choice, not a measurement of quality. Accuracy is a statement about how far the instrument may legitimately be from the true value, and it is established by comparison against a reference.
An instrument can have very fine resolution and poor accuracy. Nothing about a display reading three decimal places guarantees the third one means anything.
Where the confusion is exploited
On our micrometer pages, one listing states “an accuracy of 0.001 mm” for what is plainly its display step. A 0–25 mm (0 to 0.98 in) hand micrometer accurate to a thousandth of a millimeter would be a laboratory instrument. Another micrometer in the same hub states both figures properly: resolution 0.001 mm, accuracy ± 0.003 mm.
How to read a listing
Look for two numbers. If only one appears and it is very fine, it is almost certainly the resolution. If a maker publishes both, that alone tells you something about the listing.
This does not replace the manufacturer's instructions. Every accuracy figure, measurement category, laser class and detection depth on this page is reported from the manufacturer's own documentation and named as such — none of it is calculated here. Working near a live installation, and trusting a detector before drilling, are safety matters: follow the figures printed on your own instrument and in its manual, which take precedence over anything on this site, and where a job belongs to a qualified person, hand it to one.
What gets asked here
Which number should I compare between instruments?
Accuracy. Resolution tells you what the screen can show; accuracy tells you what the instrument can do. Two calipers displaying hundredths can have quite different tolerances.
Is finer resolution ever useful on its own?
Yes, for comparisons. A high-resolution instrument can detect that two parts differ even if it cannot say precisely what either measures — which is exactly what a zeroed caliper used as a comparator does.
Last reviewed 31 August 2026