3D Printing Tolerance Calculator
Determine the correct printed dimension for mechanical fits in 3D printing. Enter your nominal size, material shrinkage, fit type, and orientation to get a compensated target dimension ready for your slicer.
About this calculator
When a 3D printer deposits material, it shrinks slightly as it cools, and the print orientation affects dimensional accuracy differently along each axis. This calculator computes the adjusted dimension you should model or slice to, accounting for both effects. The core formula is: adjustedDimension = nominalDimension × (1 + materialShrinkage) + fitOffset × orientationFactor, where fitOffset is +0.5 mm for a loose fit, −0.3 mm for a tight fit, and 0 for a transition fit. Material shrinkage is expressed as a decimal (e.g., 0.02 for 2%). The orientation factor scales the fit offset because parts printed vertically often have better XY accuracy than Z-axis accuracy. By dialing in these values from a calibration print, you can achieve reliable press-fits, slip-fits, and clearance-fits without manual trial-and-error.
How to use
Suppose you need a 20 mm shaft hole with a loose fit, PLA shrinkage of 1% (0.01), and an orientation factor of 1.0. Step 1 – Enter nominalDimension = 20 mm. Step 2 – Enter materialShrinkage = 0.01. Step 3 – Select fitType = 'loose' (offset = +0.5 mm). Step 4 – Enter orientationFactor = 1.0. Calculation: 20 × (1 + 0.01) + 0.5 × 1.0 = 20 × 1.01 + 0.5 = 20.2 + 0.5 = 20.7 mm. Model your hole at 20.7 mm so the printed result lands close to the 20 mm loose-fit target.
Frequently asked questions
What is the difference between loose, tight, and transition fit in 3D printing tolerance?
A loose fit (clearance fit) means the shaft is noticeably smaller than the hole so parts slide freely — ideal for moving assemblies. A tight fit (interference fit) means the hole is slightly smaller than the shaft so parts must be pressed together, creating a strong mechanical bond. A transition fit sits between the two, allowing either a slight clearance or slight interference depending on manufacturing variation. In this calculator, loose adds 0.5 mm, tight subtracts 0.3 mm, and transition adds nothing to the nominal dimension before orientation scaling.
How does print orientation affect dimensional tolerance in FDM printing?
FDM printers lay down material layer by layer, so accuracy differs between the XY plane (where the nozzle moves) and the Z axis (where layers stack). XY dimensions are generally more accurate because they follow the motion system directly, while Z accuracy depends on layer height settings. Printing a hole vertically (axis along Z) tends to produce a rounder, more accurate bore than printing it horizontally. The orientation factor in this calculator lets you scale the fit offset to match the axis being printed, so you can compensate for whichever direction is less accurate on your specific machine.
Why does material shrinkage matter when calculating 3D print tolerances?
All thermoplastics shrink as they cool from the glass transition temperature to room temperature. PLA shrinks roughly 0.3–1%, ABS can shrink 1–2%, and engineering filaments like Nylon can shrink 2–3% or more. This shrinkage causes printed parts to be slightly smaller than the modeled dimension, which compounds with fit offsets to create gaps or interferences you did not intend. By multiplying the nominal dimension by (1 + shrinkage), the calculator pre-stretches the target so the finished print lands on your intended size. Measuring a calibration cube and dividing the measured size by the modeled size gives you an empirical shrinkage value to enter here.