# 3D Printing Shrinkage Calculator: Dimensional Accuracy
If you are a 3D printing enthusiast, you have likely faced this problem: you design a part with perfect measurements (for example, a 20x20x20 mm cube), you print it, and when measuring it with the caliper you discover it measures 19.7 mm. What happened? The answer is material shrinkage.Shrinkage is an inevitable physical phenomenon that occurs when thermoplastics pass from their molten state (at high temperatures) to their solid state at room temperature. As they cool, the molecules reorganize and "tighten," reducing the total volume of the part. Our shrinkage calculator is designed to help you predict this change and adjust the scale in your slicer so that your parts fit the first time.# Why do plastics shrink?
In FDM (Fused Deposition Modeling) printing, we deposit layers of hot plastic (between 200°C and 300°C) onto a surface. As the material cools, it undergoes what is known as the coefficient of thermal expansion. Basically, thermal energy keeps the molecules apart; when that energy disappears, intermolecular forces draw them closer together.Not all materials behave the same. Amorphous plastics (like PLA) have a disordered structure that tends to shrink less. In contrast, plastics that tend to crystallize or require very high temperatures (like ABS or Nylon) have a much more aggressive and difficult to control shrinkage.# Common Materials and Their Shrinkage Ranges
- ABS (Acrylonitrile Butadiene Styrene): 0.8% – 2.0%. It is one of the most difficult materials due to its high shrinkage, which often causes "warping" (deformation of the corners).
- ASA: 0.5% – 0.9%. A UV-resistant alternative to ABS with somewhat more contained shrinkage.
- Nylon (PA): 0.7% – 2.5%. Depending on whether it has carbon or glass fiber loading, its shrinkage can vary drastically.
- PETG: 0.2% – 0.5%. Very dimensionally stable, ideal for mechanical parts that do not require the thermal resistance of ABS.
- PLA: 0.1% – 0.3%. The gold standard for ease of use; its shrinkage is almost negligible for most uses.
# How to calculate the Scale Factor
Many users make the mistake of simply "adding the percentage" (if 2% is missing, they scale to 102%). However, mathematically to compensate for a loss, the scale must be slightly different. The correct formula used by our calculator is:Scale Factor = 1 / (1 - S)Where S is the shrinkage percentage expressed in decimals (e.g., 0.02 for 2%). For example, for a material that shrinks 2%, the scale factor is 1.0204, which means that in the slicer (Cura, PrusaSlicer, Bambu Studio) we must set the scale to 102.04%.
# Manual Calibration: Desired vs. Real Measurement
The inverse calibration process is simple: print a test object with a known measurement (e.g., a 100mm calibration cube). Once it is completely cool (waiting at least 30 minutes is crucial), measure the part with a digital caliper. Enter both values into the calculator and it will give you the exact adjustment percentage for that filament spool.# Non-Uniform Shrinkage: The X, Y, and Z Axes Problem
In 3D printing, physics is not the same in all directions. Because layers are deposited on top of each other, interlayer adhesion in the Z axis usually limits vertical shrinkage. Normally, you will find that measurements in the horizontal plane (X and Y axes) require more compensation than height (Z axis).Pro Tip
If you are working with nylon or technical materials, always measure the part 24 hours after printing. Some plastics absorb environmental moisture and can "swell" slightly after cooling, altering the final measurement.
# Factors that affect final accuracy
- Extruder Temperature: At higher temperatures, the material enters more expanded but also usually suffers more sudden cooling.
- Bed Temperature: A hot bed prevents the base of the part from shrinking faster than the top, reducing warping.
- Infill Density: Very dense parts have more plastic mass exerting internal shrinkage force towards the center.
- Layer Fan: In materials like ABS, too strong a fan can cause cracks and excessive, irregular shrinkage.