Your FDM parts print smaller than the model — and holes shrink even more than walls. Measure a test print, get the exact slicer scale factor, then dial in press-fit, snug, sliding and loose clearances with a hole & pin compensator built for real FDM behaviour.
Two ways to get your scale factor: measure your own test print (most accurate) or use a material preset (good starting point).
Pick how the parts should behave, pick your material, and get a per-side clearance recommendation. High-shrink materials (ABS, ASA, Nylon) automatically get a small extra allowance.
Press fit is modelled as interference (negative = hole smaller than shaft).
| Material | Press fit | Snug | Sliding | Loose |
|---|
Holes print undersized — more than outer walls shrink. Enter the shaft/pin diameter and the fit you want; the calculator adds clearance and hole-undersize compensation, then scales for shrinkage.
Community-typical FDM shrinkage values. Treat every number as a starting point, not a guarantee.
| Material | Typical | Range | Hole undersize | Clearance adj. | Notes |
|---|
The 3-step loop that beats any table: print → measure → compensate. Do it once per material and your fits become repeatable.
Printed a test hole at a compensated diameter but it still missed? Enter what happened and get a corrected compensation value.
Every number on this page comes from three transparent formulas — no black boxes:
Hole compensation is additive (a fixed mm amount) because holes print undersized by a roughly constant amount regardless of diameter, while shrinkage is multiplicative (a percentage). Clearance recommendations are per-side rules of thumb from FDM community practice: press −0.05 mm (interference), snug +0.15 mm, sliding +0.25 mm, loose +0.40 mm, with +0.05 mm for ABS/ASA/PC and +0.10 mm for Nylon. Applied together, multiplicative shrinkage compensation plus additive hole compensation is what restores dimensional accuracy to FDM assemblies.
As extruded plastic cools from printing temperature to room temperature, it contracts. A part modelled at exactly 100 mm might print at 99.7 mm in PLA or 99.3 mm in ABS. That small percentage is invisible on decorative prints but ruins assemblies: shafts won't enter holes, lids won't close, and multi-part prints won't mate. Measuring your shrinkage and scaling the model up by the matching factor (tab 1) compensates for it.
Typically 0.2–0.5%, with about 0.3% a common working value. That means a 100 mm PLA part usually prints between 99.5 and 99.8 mm. PLA is the most dimensionally forgiving common filament, which is why it is a good choice for parts that must fit together. Your exact number depends on your printer and temperatures — measure a test print rather than trusting the typical value blindly.
Typical ABS shrinkage is 0.5–1.0% (ASA is similar at 0.6–1.0%); PETG runs 0.3–0.6%, polycarbonate 0.3–0.6%, and Nylon (PA) 0.8–2.0% — the highest and least predictable of the group. ABS and ASA also warp if printed without an enclosure, which changes effective dimensions beyond simple shrinkage. The full table with hole-compensation defaults is in the Material database tab.
Print a test part of known size, let it cool to room temperature, and measure it with calipers. Divide the nominal (modelled) size by the measured size: scale = nominal ÷ measured. Example: a 75 mm cube measures 74.5 mm, so the scale is 75 ÷ 74.5 = 1.0067 — enter 100.67% in your slicer's X/Y scale fields. Tab 1 does this math for you, including a separate Z factor.
Two effects stack: the whole part shrinks as it cools, and holes additionally print undersized because the extruded arcs get pulled slightly inward and over-extrude into the opening. In practice holes come out roughly 0.1–0.3 mm smaller than modelled, almost regardless of hole diameter. That is why this calculator compensates holes additively (a fixed mm amount) while shrinkage is compensated multiplicatively (a percentage).
Design the hole about 0.05 mm smaller per side than the shaft (interference fit) so the parts lock by friction, then add hole-undersize compensation and shrinkage scaling on top — tab 3 computes the final model diameter. Assemble with a clamp or mallet, never force beyond what the layer bonds can take. Polycarbonate holds press fits extremely well, so keep interference small there.
A good starting point is 0.25 mm per side (0.5 mm on the diameter) for PLA, PETG and TPU, plus about 0.05 mm extra per side for ABS, ASA and polycarbonate, and 0.10 mm extra for Nylon. Hinges, rails and drawers in that range move with light resistance instead of binding. For parts that must never bind — bolts passing through, pivots — use the loose fit of 0.40 mm per side.
Often, yes. Z shrinkage is usually smaller because each layer is constrained by the one below and the bed, while X/Y can contract more freely. Measure a test cube's height separately from its width and enter both in tab 1 — the calculator gives you independent X/Y and Z factors. Most slicers let you set per-axis scaling.
The first few layers get squished wider than the rest of the part because the nozzle presses them against the bed. If you measure those layers, your shrinkage reading will be wrong (the part can even measure larger than modelled). Always measure mid-part, and keep fit features a few layers above the base or add a small chamfer to the bottom edge.
Both attack the same problem differently. Horizontal expansion (called XY compensation in some slicers) shifts every wall inward or outward by a fixed amount, which also changes outer dimensions. This calculator's additive hole compensation targets holes specifically. Pick one method — stacking both double-compensates and your holes will print oversize.
Plastic keeps moving after printing: it finishes cooling, internal stresses relax, and hygroscopic materials like Nylon absorb moisture from the air and swell or warp. For fits that matter, let the part rest at room temperature for 24 hours before the final test-fit, and store Nylon parts dry.
Partially. Resin also shrinks — typically 1–3% during printing and post-curing — but hole behaviour and the compensation values differ from FDM, and every resin formulation behaves differently. Use tab 1's measurement mode with your own test print and a custom shrinkage override in tab 3 rather than the FDM material presets.
No. They are workshop rules of thumb for hobby and prototyping use, not engineering tolerances. Anything load-bearing, safety-relevant, or produced at volume needs proper tolerance analysis and testing on your actual process. This tool helps you get close fast; your test-fit is the final authority.
Print a 20 mm calibration cube with your normal profile, let it cool completely to room temperature, and measure with digital calipers across the middle of each face — not near the base. Average the X and Y readings, and measure Z separately. One careful measurement beats five rushed ones.
Because a single number would be dishonest. Shrinkage varies with your printer, the spool, enclosure and room temperature, so the calculator shows the model dimension for the material's typical value plus the band spanned by its min–max range. Print your own test part to collapse that band to your printer's real number.
No. The entire tool — math, material database and all — runs locally in your browser as a single HTML file. There are no network requests, no analytics calls, no cookies and no sign-up. Your dimensions never leave your device.
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