Guide · Measuring
How to measure parts with calipers for 3D printing
A replacement part is only as good as the measurements behind it. Digital calipers (around 15–30 €) measure to 0.01 mm, which is more than enough for FDM printing — if you use them correctly. These are the techniques that matter for functional parts.
- Tool
- Digital calipers, 150 mm
- Resolution
- 0.01 mm (accuracy ±0.02–0.03 mm)
- Rule
- Measure 3 times, use the average
- Most important
- Measure the mating part, not the broken one
Start a partFirst part free · no credit card
The four caliper functions
| Function | Jaws | Use for |
|---|---|---|
| Outside | Large lower jaws | Shafts, pins, thickness, outer diameter |
| Inside | Small upper jaws | Holes, slots, inner diameter |
| Depth | Rod at the end | Hole depth, how deep a shaft goes in |
| Step | Jaw end faces | Shoulders, height differences |
Step by step
- 01Zero the calipers with the jaws closed and clean.
- 02Hold the part square to the jaws; for round parts rotate slightly and take the largest value (outside) or smallest (inside).
- 03Measure each dimension three times at different positions and average.
- 04For D-shafts measure the round diameter and the distance from the flat to the opposite side.
- 05For hole patterns measure edge-to-edge of two holes and add one hole diameter to get the centre distance.
- 06Write down which values are fit-critical and give those to FitPrint exactly.
Common mistakes
- Measuring the worn or broken part instead of the part it mates with.
- Squeezing soft materials (rubber, foam, cables) — measure with light pressure.
- Tilting the calipers in a hole, which reads too small.
- Forgetting that a phone case adds 1.5–2 mm per side.
Frequently asked questions
Can I measure with a ruler instead?
For non-critical sizes yes; for anything that has to fit (holes, shafts, slots) a ruler's ±0.5 mm is not enough.
Can AI measure from a photo?
From a photo with a reference object (credit card, coin, ruler) an AI can estimate sizes to a few percent — fine for proportions, not for fits. FitPrint uses photos for shape and asks for caliper values where precision matters.
Related
Updated · Generated parts are a starting point — always test-fit before relying on a part.