3D Print Tolerance Calculator
Calculates the adjusted target dimension for 3D printed parts to achieve a specific mechanical fit, accounting for printer accuracy, material shrinkage, and surface finish. Use it when designing mating parts like shafts, holes, and sliding joints.
About this calculator
When two 3D printed parts must assemble together, the nominal CAD dimension rarely produces a perfect fit straight off the printer. Printer accuracy, post-print material shrinkage, and surface roughness all introduce dimensional error that must be compensated in the design file. The adjusted dimension formula used here is: adjustedDimension = nominalSize + (fitType + printerAccuracy × surfaceFinish + nominalSize × materialShrinkage / 100). The fitType term encodes a signed offset for the class of fit desired—clearance, transition, or interference. Multiplying printerAccuracy by a surfaceFinish factor scales the accuracy penalty by how rough the printed walls are. The shrinkage term scales with nominal size because larger parts shrink more in absolute terms. Together these offsets tell you the exact dimension to model in your CAD software to achieve the intended real-world fit.
How to use
Suppose your nominal hole diameter is 20 mm, the fitType offset is 0.3 mm (clearance fit), printerAccuracy is 0.9, surfaceFinish factor is 0.1, and material shrinkage is 0.5%. Calculate: shrinkage term = 20 × 0.5 / 100 = 0.10 mm; accuracy term = 0.9 × 0.1 = 0.09 mm; total offset = 0.3 + 0.09 + 0.10 = 0.49 mm; adjustedDimension = 20 + 0.49 = 20.49 mm. Model your hole as 20.49 mm in CAD and the printed result should land close to the 20 mm target fit.
Frequently asked questions
How much tolerance should I add for a 3D printed clearance fit between a shaft and hole?
A typical starting point for a loose clearance fit on a desktop FDM printer is 0.2–0.4 mm of total diametrical clearance, meaning the hole diameter is modeled 0.2–0.4 mm larger than the shaft. Tighter-tolerance machines like resin SLA printers can achieve fits with 0.05–0.1 mm clearance. Material also matters—PETG tends to print slightly oversize compared to PLA, so you may need less added clearance. Always print and test a calibration coupon before committing to a full print run.
Why do 3D printed parts shrink after printing and how much should I account for?
Thermoplastics expand when melted and contract as they cool back to room temperature. FDM parts continue to relax slightly after leaving the print bed as residual thermal stresses equalize. PLA typically shrinks 0.2–0.5% linearly; ABS can shrink 0.5–0.8% or more, especially without an enclosure. This means a 100 mm part in ABS may measure 99.5–99.2 mm after cooling. For precision assemblies, entering your measured shrinkage percentage into this calculator automatically compensates by scaling the modeled dimension upward, so the printed result lands on your nominal target.
What is the difference between clearance, transition, and interference fits in 3D printing?
These three classes describe how tightly two mating parts are intended to assemble. A clearance fit has guaranteed space between parts, allowing free rotation or sliding—used for axles, hinges, and snap-together enclosures. A transition fit hovers near zero clearance and may require light hand pressure to assemble, offering better alignment with minimal play—common for locating pins. An interference fit (press fit) means the shaft is nominally larger than the hole, requiring force or heat to assemble, which locks parts together rigidly without fasteners. In this calculator the fitType field encodes a signed offset representing each class, with positive values for clearance and negative values for interference.