3D Print Tolerance & Fit Calculator

A well-calibrated FDM printer holds about ±0.2 mm in XY and ±0.1-0.2 mm in Z. SLA/DLP achieves ±0.1-0.15 mm, and SLS lands around ±0.3 mm. But several things push those numbers around.

• Nozzle size. A 0.4 mm nozzle produces line widths of about 0.4-0.5 mm, which sets the minimum resolution of any feature. Switching to a 0.25 mm nozzle tightens things up but costs print time.
• Material. PLA is dimensionally stable and predictable. ABS and Nylon shrink more (see the shrinkage calculator). Semi-crystalline materials have higher variance between prints.
• Calibration. Belt tension, e-steps, flow rate, and first-layer squish all affect dimensional accuracy. A tolerance test only means something on a calibrated machine.
• Part geometry. Large flat surfaces warp more. Small holes print tighter than modeled (FDM holes are typically 0.1-0.3 mm undersized due to the nozzle path). Tall thin features lean. The fit values in this calculator assume compact, well-supported geometry.
• Extrusion width rule. AON3D recommends basing your clearance on extrusion width: 1x extrusion width (~0.4 mm for a 0.4 mm nozzle) for a sliding fit, 2x for a free-running fit. This scales naturally with nozzle size.

The values in this calculator are good starting points, but every printer is a little different. Here is how I find my exact numbers for a given material.

1. Print a tolerance test: a block with a 10 mm pin and holes at 10.0, 10.1, 10.2, 10.3, 10.4, and 10.5 mm.
2. Try fitting the pin into each hole. Note which ones are too tight, which slide, and which are loose.
3. The smallest hole the pin slides into freely is your sliding fit clearance. The one before it is your transition fit.
4. Use those values here and adjust the safety margin slider until the calculator matches your measurements.

Repeat this whenever you change materials or make mechanical changes to your printer (new nozzle, belt retensioning, firmware update). The numbers drift.