How to Read a Micrometer: Simulator
How to Read a Micrometer Screw Gauge: Interactive Simulator
Turn the virtual micrometer, guess the reading, then check your answer with the full working. Resolution 0.01 mm, with random practice questions.
Drag the thimble with a mouse or finger, use the slider, or click the drawing and press the arrow keys (1 press = 0.01 mm, Shift + arrow = 0.5 mm). When zoomed in, swipe elsewhere on the drawing to scroll.
What is a micrometer screw gauge?
A micrometer screw gauge measures length to 0.01 mm using a precision screw: one full turn of the thimble moves the spindle 0.5 mm, and the thimble is divided into 50 parts. It is about ten times more precise than a 0.1 mm vernier caliper, ideal for small and thin objects.
Parts of a micrometer
| Part | Use |
|---|---|
| U-shaped frame | Holds everything. Hold it by the insulating plates so hand heat does not expand it. |
| Anvil | Fixed face the object rests against |
| Spindle | Moves in and out to grip the object |
| Lock | Locks the spindle so the reading does not change |
| Sleeve (main scale) | Millimetres above the datum line, half-millimetres below it |
| Thimble | Scale 0–49 (50 divisions), 0.01 mm each |
| Ratchet | Turns the spindle with constant force and clicks when the object is gripped |
How to use a micrometer
- Clean the anvil and spindle faces.
- Check zero error: close it with the ratchet until it clicks; the thimble 0 should sit on the datum line.
- Open the spindle slightly wider than the object.
- Place the object between the anvil and spindle.
- Turn the thimble until the spindle nearly touches, then finish with the ratchet until it clicks two or three times.
- Lock the spindle.
- Read the sleeve and thimble and add them.
- Correct for zero error.
- Repeat at several points and average.
- Store it clean with the faces slightly apart.
How to read a micrometer
- Sleeve, upper scale: the last millimetre line still visible left of the thimble edge.
- Sleeve, lower scale: if the next half-millimetre line is visible, add 0.5 mm.
- Thimble: the line that sits on the datum line, times 0.01 mm.
- Add them.
Worked examples
Example 1
The sleeve shows 4 mm, the next half-millimetre line is not visible and thimble line 23 is on the datum line.
- Sleeve = 4 mm
- Thimble = 23 × 0.01 mm = 0.23 mm
- Reading = 4 + 0.23 = 4.23 mm
Answer: 4.23 mm.
Example 2
The sleeve shows 7 mm and the next half-millimetre line is visible. The thimble reads 28.
- Sleeve = 7 + 0.5 = 7.5 mm
- Thimble = 28 × 0.01 mm = 0.28 mm
- Reading = 7.5 + 0.28 = 7.78 mm
Answer: 7.78 mm, written (7.780 ± 0.005) mm.
Example 3: zero error
With the faces closed the micrometer reads +0.02 mm. A wire reads 3.46 mm. What is its true diameter?
- Zero error = +0.02 mm
- True diameter = 3.46 − 0.02 = 3.44 mm
Answer: 3.44 mm.
Common mistakes
- Forgetting the 0.5 mm when the lower half-millimetre line is visible, or adding it when it is not yet visible (watch thimble readings of 45–49).
- Tightening with the thimble instead of the ratchet, which squeezes the object.
- Parallax.
- Skipping the zero check or measuring dirty surfaces.
Micrometer or vernier caliper?
| Vernier caliper | Micrometer | |
|---|---|---|
| Resolution | 0.1 / 0.05 / 0.02 mm | 0.01 mm |
| Typical range | 0–150 mm | 0–25 mm per instrument |
| Measures | length, outside and inside diameter, depth | thickness and outside diameter |
| Example | test-tube diameter, hole depth | paper thickness, wire diameter |
Try the vernier caliper simulator too.
For tips on measuring workpieces, see also our guide to using a micrometer screw gauge.
Frequently asked questions
What is the resolution of a micrometer?
An analogue micrometer reads to 0.01 mm: a 0.5 mm screw pitch divided into 50 thimble divisions. Some digital micrometers read to 0.001 mm.
What is a micrometer used for?
Measuring the thickness of thin objects (paper, sheet metal, glass slides) and the outside diameter of small objects (wire, cable, small bolts, marbles) to 0.01 mm.
What is the formula for a micrometer reading?
Reading = sleeve reading + (thimble line on the datum line × 0.01 mm). The sleeve reading includes 0.5 mm when the half-millimetre line is visible.
What does the ratchet do?
The ratchet limits the turning force. Once the object is gripped it clicks and slips, so every measurement uses the same pressure.
Why does the thimble have 50 divisions?
One full turn advances the spindle 0.5 mm, so each of the 50 divisions is 0.5 ÷ 50 = 0.01 mm.
What is zero error on a micrometer?
If the thimble 0 is not on the datum line when the anvil and spindle touch, there is a zero error. Subtract it from every reading.
Equipping a laboratory?
AMI Scientific supplies chemicals and laboratory equipment to universities, research labs and industry, with formal quotations and tax invoices. Send us your equipment list and our team will prepare a quotation.
Other measuring and lab equipment: vernier caliper, analytical balance, graduated cylinder, volumetric flask, burette, thermometer, laboratory equipment and their uses.
