Dimensional Accuracy
Diagnose wrong part dimensions by separating flow, first-layer shape, sliced height, material shrinkage, and undersized holes.
Use this guide when a cooled part does not match the intended dimensions or fit. A small hole, a widened base, and a uniformly shrunken part need different corrections. Measure the pattern before changing scale or flow.
Acceptable deviation depends on the drawing, fit, material, geometry, and measurement method. A single error threshold cannot establish that a printer is working correctly or that an axis has missed steps.
1. Measure a Repeatable Baseline
- Check model units, imported dimensions, and object scaling in the slicer. Save the project and profile copies.
- Use dry filament and a tuned material profile. Resolve excess material or intermittent feeding before measuring for compensation; see Material Tuning.
- Let the part cool to a consistent measurement condition. If it is annealed or conditioned after printing, compare its intended final state consistently.
- Measure X, Y, and Z separately. Avoid seams, burrs, and a widened bottom edge when measuring main walls.
- Measure holes separately. Repeat measurements and print another sample to check repeatability.
- Compare at least two nominal feature sizes before concluding that an error is proportional shrinkage.
Choose the Correction
| Measurement or appearance | Next check |
|---|---|
| Only the bottom edge is wider | Elephant's Foot |
| Swollen walls and raised solid-layer ridges | Over-Extrusion |
| Only height differs slightly and consistently | Compare the model with the sliced layer heights |
| Similar percentage error across different sizes | Investigate shrinkage after checking scale |
| External size is correct but holes are tight | Hole geometry and local compensation |
| Measurements vary between identical prints, or bands and shifts appear | Motion and feeding before compensation |
2. Compare Model Height with Sliced Height
For a flat-topped part printed directly on the plate at constant layer height, the nominal stack is:
stack height = first layer height + n × layer height
Here, n is the number of layers after the first. A 0.24 mm first layer followed by 199 layers of 0.20 mm gives 40.04 mm. This describes that stack; it does not predict which layer count the slicer will choose for every model.
Inspect the actual preview and top layer's Z position. Account for variable layer height, rafts, support gaps, and existing Z compensation before comparing with CAD height.
If the difference is already present in the sliced height, try a suitable layer-height combination and re-slice. Stay within the nozzle/profile's supported range and verify the first layer afterward. Do not select first-layer height solely from the last decimal digits of the model dimension or use Babystepping to correct the whole part's height.
If sliced height is correct but the cooled print differs, continue with repeatability and shrinkage checks. For inconsistent first-layer squish, use First Layer Calibration.
3. Estimate Material Shrinkage
Contraction is a possible explanation when a sound print is consistently smaller and its error grows with nominal size. Check X and Y separately before combining them into one XY correction. Unequal axis errors can also require alignment or mechanical investigation.
For an uncompensated baseline, calculate the measured shortfall per axis:
shortfall (%) = (nominal size − measured size) ÷ nominal size × 100
A 100 mm dimension measured at 99.5 mm has a 0.5% shortfall. A 50 mm dimension measured at 49.75 mm has the same percentage shortfall, supporting investigation of a proportional correction. This estimate does not prove that all error comes from shrinkage.
Save a separate material profile. In versions that provide Shrinkage compensation, locate it in the filament settings and check the field's units and tooltip. Check whether XY and Z are separate and whether the field expects shrinkage percentage or scale. The feature's introduction is documented in the official PrusaSlicer release notes; use the controls supported by your installed version.
Shrinkage percentage and enlargement percentage are not interchangeable. For the example above, direct geometric scaling would use 100 ÷ 99.5 ≈ 1.005025, or about 100.5025%. Do not apply both object scaling and material compensation for the same error.
Record the baseline, adjust one compensation at a time, re-slice, and repeat both sizes. If compensation was already enabled, do not blindly replace it with the remaining shortfall. Keep drying, temperatures, orientation, and cooling conditions consistent.
4. Correct Holes Separately When Needed
If flow is calibrated and outside dimensions are correct but holes remain too small, avoid reducing flow further. Compare hole dimensions at several heights to exclude a bottom lip. Inspect the model and preview for faceted geometry or a deformed horizontal-hole roof.
Use hole-specific compensation if your slicer provides it, or a measured design allowance for the fit. General XY contour compensation can affect inner and outer boundaries; check both afterward. It is not interchangeable with proportional material shrinkage correction.
Test the relevant hole sizes and mating features. Check fit after cooling alongside external dimensions and wall integrity.
Verify the Result
Repeat with the saved profile and measure after cooling. Accept a correction only when it repeats and meets the required fit without gaps, weak walls, or a distorted base.
If identical jobs give different dimensions, or height loss accompanies bands or abnormal motion, use Z-Wobble and Layer Shifting as appropriate. Do not change motor steps or driver settings to compensate for unexplained material or slicing errors.
Keep the model, slicer project, nominal and measured dimensions, compensation baseline, material batch, nozzle, and thermal conditions. Include repeated measurements and photos if support needs to investigate.
FAQ
Support
If you could not find an answer here, reach out to our support team.