3D Print Shrinkage, Scale & Hole Compensation Calculator

How it works

shrinkage % = (1 − measured ÷ designed) × 100 · scale = 100 ÷ (100 − shrinkage) · design hole = (target + undersize + fit clearance) × scale

Thermoplastics contract as they cool from the nozzle or cure in the vat, so a part comes out slightly smaller than the model, and the fix is to scale the model up by the reciprocal of the shrinkage — a measured test cube is far better than a table value because flow rate, temperature and cooling change the result on every printer. Holes suffer an extra, geometric error: a circle is sliced into a polygon whose flats sit inside the true circle, the bead squishes outward, and the first layer spreads, so holes print undersize by a few tenths of a millimetre regardless of shrinkage. Adding that allowance and the clearance the fit needs before scaling gives a design diameter that comes out right the first time.

Worked example

A 20 mm calibration cube that measures 19.85 mm has shrunk 0.75%, so scale the model to 100.756% in X and Y. For a shaft of 8 mm to turn freely (0.25 mm clearance) on a printer whose holes come out 0.25 mm small, model the hole at (8 + 0.25 + 0.25) × 1.00756 ≈ 8.56 mm; for an exact 8 mm hole, 8.31 mm.

Frequently asked questions