3D printing shrinkage calculator: the CAD size that prints right
Pick a process, material, axis and size and get what to draw in CAD, or what the model will print as. X/Y and Z are separate, and holes have their own compensation.
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- 10 materials7 for FDM, 2 resins, 1 for SLS
- X/Y and Z aparttwo axes, two figures
- +0.2 mm on a holeextra on FDM, on the diameter
- Test cube calibrationyour own shrinkage percentage
What 3D print shrinkage is
This 3D printing shrinkage calculator from EduFacturing is a free online tool that works out what size to draw in the CAD model to get the size you want after 3D printing. It works both ways: from the size you want to the model, and from the model size to the expected printed one.
Nine of the 10 materials carry a published range in X/Y and in Z, a typical value, a source and a confidence level; TPU has no reliable range. The calculator uses the typical value, and a cube calibration replaces it with your own percentage.
What it works out: CAD size and printed size
Shows how much each material shrinks
PLA, PETG, ABS, ASA, nylon, PC and TPU for FDM, two resins for SLA/DLP and PA12 for SLS. Nine have X/Y and Z apart, with a source and a confidence level; TPU has none.
Works out the CAD size and the printed size
Pick the direction, an outside size or a hole diameter, and the axis. The result is in mm to the hundredth: “Draw in CAD” or “Expect after printing”.
Adds a hole offset for FDM
An FDM hole gets 0.2 mm added to its diameter on top of the thermal compensation. The figure is derived from the EduFacturing rules core and shown on screen.
Calibrates from a test cube
Enter the cube's nominal size and the measured X, Y and Z. You get your own percentage for X/Y and for Z and can use it instead of the catalog one.
When you need a shrinkage calculator
Shrinkage is fractions of a percent, but in an assembly it shows up in tenths of a millimetre.
An assembly of two parts
A pin and a hole, or a lid and a body. In PLA on FDM, in X/Y, an outside size of 50 mm is drawn at 50.15 mm and a 10 mm hole at 10.23 mm.
A finished model: what will print
You know the CAD size and want what will print: 50 mm in PLA gives 49.85 mm in X/Y.
A new material or printer
Print a 20 mm cube and measure it with calipers. Readings of 19.94, 19.92 and 19.88 mm give 0.35% in X/Y and 0.60% in Z.
Choosing a material
At 50 mm and the typical X/Y shrinkage you draw from 50.15 mm for PLA to 50.76 mm for Tough resin.
How the CAD size is worked out
Everything runs from one shrinkage percentage s for the chosen axis: the typical catalog value or your own from calibration.
Shrinkage
The typical value for the material and the axis, or the percentage from calibration if you switched it on.
Size
The size you want is divided by (1 − s/100) to give the CAD size; in reverse, the model size is multiplied by (1 − s/100). Outside sizes and holes are both larger in the model.
Holes on FDM
0.2 mm is added to the hole diameter, and subtracted in the reverse direction. Resin and SLS get no such offset.
Checks
For a target size, a shrinkage of 100% or more is refused as impossible. A calibration outside −3% to 8% is shown with a warning.
| Applies to | Formula | Meaning |
|---|---|---|
| Model for a target size | model = target / (1 − s / 100) | for an outside size |
| What will print | printed = model · (1 − s / 100) | for an outside size |
| Hole on FDM | model = target / (1 − s / 100) + 0.2 | diameter in mm; in reverse: model · (1 − s / 100) − 0.2 |
| Calibration | s = (nominal − measured) / nominal · 100 | per axis; X/Y is the mean of X and Y |
X/Y and Z apart, holes, test cube
X/Y and Z are separate figures
The nine materials with data shrink differently on the two axes (PLA typically 0.3% and 0.6%), so the axis is a choice.
No figure without data
TPU has no reliable range, and the calculator gives no number without a calibration.
It does not calculate warping: that depends on the geometry, orientation, cooling air and bed adhesion, and has no reliable formula in millimetres. It does not separate thermal shrinkage from process shrinkage: a cube calibration gives them combined.
The percentages are typical values from public guides cited in the code (Prusa and Ultimaker/Cura for PLA, Formlabs for the resins, EOS for PA12, slicer guides and manufacturers for the rest), not measured on your printer. Calibrate for an exact result.
Questions about PLA, ABS and nylon shrinkage
How much does PLA shrink after printing?
PLA shrinks 0.2–0.5% in X/Y and 0.4–0.8% in Z. ABS: 0.4–0.8% and 0.7–1.5%; nylon: 0.3–1.5% and 0.5–2.0% with low confidence. Tough resin: 1.0–2.5% in X/Y. These are typical ranges from public guides, as in the tool.
How to compensate for shrinkage in 3D printing?
The size you want is divided by (1 − s/100), where s is the shrinkage in %. For 50 mm in PLA (X/Y, typically 0.3%) the model is 50.15 mm. In reverse, 50 mm in the model gives 49.85 mm.
Why are 3D printed holes too small, and how large do I draw them?
Because the material around a hole shrinks too, so the model hole must be larger. On FDM another 0.2 mm is added to the diameter: a 10 mm hole in PLA is drawn at 10.23 mm in X/Y.
How to calibrate from a test cube?
Print a cube of known size, measure X, Y and Z with calipers and enter the four numbers. X/Y is the mean of X and Y. Then tick the box to use the calibration; changing the process or material switches it off.
Why is there no figure for TPU?
There is no reliable published range: shrinkage depends on Shore hardness, speed and cooling. The calculator asks for a calibration instead of a misleading number.
The 3D printing shrinkage calculator is free. Pro opens the rest
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Work out the size for your material
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