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How to read a dial caliper

Updated: 22 October 2026

The jaws are on the part, the needle has stopped, and you are not sure whether the size is the beam, the dial, or both. The reading is a sum. This is how to read a dial caliper when the face is already in millimetres and the open question is whether one turn is 1 mm or 2 mm. The three listings, and who each one is for, are on the [Dial caliper](/hub/measuring-and-marking-tools/dial-caliper) comparison. Peter F. used the National Physical Laboratory calliper guide and the listing notes. A qualifying purchase can earn a commission at no extra cost to you.

The jaws are on the part, the needle has stopped, and you are not sure whether the size is the beam, the dial, or both. The reading is a sum.

Our top picks

Mitutoyo Mitutoyo 505-732 dial caliper

Best overall

Mitutoyo Mitutoyo 505-732 dial caliper
9.3/10about £86.71
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Standard Gage Standard Gage dial caliper, 150 mm

Best value

Standard Gage Standard Gage dial caliper, 150 mm
9.3/10about £45.99
View offer
Hyuduo Hyuduo plastic dial caliper, 150 mm

Alternative

Hyuduo Hyuduo plastic dial caliper, 150 mm
5.4/10about £12.71
View offer
On this page
  1. 1.Beam, then dial
  2. 2.One turn can be 2 mm or 1 mm
  3. 3.Set zero, then look straight down
  4. 4.When you stop

Beam, then dial

Read the beam first. Each main mark on a metric beam is 1 mm. Take the last whole millimetre the moving jaw has gone past, and leave the millimetre it has not reached. Wonkee Donkee's guide puts the order in one line: read the beam in whole millimetres, then read the dial, then add. The dial does not replace the beam. Look at the centre of the dial before you add, because the fraction depends on the graduation printed there. If the title said 150 mm and the face looks like inches, go to metric or imperial dial caliper before you add anything. The National Physical Laboratory's calliper guide treats 0.02 mm as the typical metric dial mark, and 0.01 mm as the finer class. The contact has to be square.

One turn can be 2 mm or 1 mm

The National Physical Laboratory's table calls a 0.02 mm dial a DT-type: one revolution is 2 mm. It calls a 0.01 mm dial a DE-type: one revolution is 1 mm. On the 2 mm dial the needle passes zero twice while the jaws open 2 mm. The second half is still a positive millimetre. It is not a minus reading. On the Standard Gage listing the bullets state 0.02 mm, and one review says one turn is 2 mm because the gearing follows an inch layout remarked for metric. That description is not a measurement of the amazon.co.uk tool. Reviews of the Mitutoyo 505-732 listing describe 0.01 mm marks and one full turn per millimetre. The listing's accuracy line is still 0.002 in, so do not treat the Amazon text as the manufacturer's millimetre specification. If you cannot see 0.02 mm or 0.01 mm in the centre of the face, stop and identify the unit first.
Mitutoyo Mitutoyo 505-732 dial caliper

Testsieger

Mitutoyo Mitutoyo 505-732 dial caliper
9.3/10about £86.71
View offer

Set zero, then look straight down

Wipe the oil film off the jaws before the first reading, and keep chips out of the rack. Mitutoyo's instructions say the rack drives the needle, and chips can skip the pointer. Close the jaws gently. Look square at the face, not from the side, and turn the bezel until the needle sits on zero. A side view is parallax: the needle appears to sit on a mark it has not reached. Reviews of the Standard Gage dial say the bezel can be reset from the instructions. Zero against clean closed jaws, not against the part. Open and close once more and see whether zero returns. Lock the slide if you need to turn the tool towards the light, then read the beam and then the dial. Usual reference temperature for this class of instrument is 20 °C. Let the tool and the work sit together before you read.

When you stop

Stop if the needle jumps, stutters or misses zero after a clean close. The National Physical Laboratory's guide says dirt in the rack lets the pinion jump so the needle misses zero. Wipe what you can see on the beam and try zero again. This page does not include a tooth-reset procedure. If zero still will not repeat, the reading is not a size you should machine to. Stop as well if the centre of the dial is in inches. That is the wrong instrument for a millimetre total. Hand the job to someone who calibrates instruments when a drawing states a tolerance tighter than a workshop check.

Common questions

Do you read the beam or the dial first?
Read the beam first, and take the last whole millimetre the jaw has passed. Then read the dial and add that fraction. Wonkee Donkee's metric guide uses that order. The needle never replaces the beam. A dial that shows 0.66 mm is only 0.66 mm until you add the whole millimetres already on the scale.
What is one mark on a typical metric dial?
On a typical metric workshop dial one mark is 0.02 mm, which is the resolution the National Physical Laboratory treats as usual. A finer metric face is marked in 0.01 mm. The mark size is not the stated error.
Why does the needle pass zero twice in 2 mm?
Because a 0.02 mm dial is built so that one revolution equals 2 mm. The National Physical Laboratory calls that a DT-type. Mitutoyo's instructions put it as half a turn per main-scale millimetre. The second pass through the marks is the next millimetre, still positive. A 0.01 mm dial typically uses one full turn for a single millimetre.
How do you zero the bezel?
Wipe the jaws, close them gently, look straight at the face, and turn the bezel until the needle sits on zero. Open and close again to see whether zero returns. On the Standard Gage listing, reviewers say the bezel can be reset from the instructions. Zero against clean jaws, not against the part you are about to measure.
What if zero does not repeat?
Do not record a size. Dirt in the rack can let the pinion jump, which is the warning in the National Physical Laboratory guide and in Mitutoyo's chip note. Wipe the beam and try again. If the needle still misses zero, stop. There is no tooth-reset procedure on this page.

Related pages

Dial caliper buying guide

Best dial caliper

Dial caliper

Metric or imperial dial caliper: check the face first

Dial caliper vs digital caliper: a needle or screen

Sources

Public sources listed for this comparison, checked against the 20 October 2026 shelf notes. Prices, stars and review counts for the three ASINs are the amazon.co.uk figures in that set. We did not run a lab test.

  1. NPL MGPG 40, calliper guide (retrieved October 2026)
  2. BSI BS EN ISO 13385-1:2019 (retrieved October 2026)
  3. ISO 13385-1:2019 (retrieved October 2026)
  4. Mitutoyo UK 505-732 (retrieved October 2026)
  5. Mitutoyo dial caliper instructions (retrieved October 2026)
  6. Wonkee Donkee, reading a metric dial caliper (retrieved October 2026)
  7. RS PRO 150 mm dial caliper 307-4666 (retrieved October 2026)
  8. Consumer Rights Act 2015, section 11 (retrieved October 2026)