3D Print Tolerance & Clearance Calculator
How much clearance a printed fit really needs — where the 0.2 mm rule comes from, and the size at which it stops working.
Where a flat rule stops working
Where the 0.2 mm rule comes from — and where it stops
A printed feature is off by about 0.05 mm per surface from extrusion geometry, and the error runs the same way on both halves of a fit: external features come out oversized and internal ones undersized. So a nominal 10 mm peg prints 10.10 and the matching hole prints 9.90 — 0.20 mm of interference before anybody has designed in any clearance at all. That's exactly the number everyone quotes, it's four surfaces of error, and it buys a press fit rather than a sliding one.
But it's only a constant below the crossover. Thermal shrinkage adds an error proportional to the dimension, so the clearance you need is 0.20 mm fixed plus twice the shrinkage plus the gap you actually want. Those two terms are equal at 33 mm in PLA, 25 in PETG, 17 in ASA, 14 in ABS and 8 in nylon. Below that the flat rule does the right thing; above it, it's short — by 0.24 mm at 50 mm in PLA and 0.54 mm at 100 mm, which is the difference between a part that assembles and one that needs a file.
Which means the flat rule is really a PLA rule. It survives because most printed features are under 33 mm, and it quietly stops working in materials that shrink more. ABS's reputation for being dimensionally difficult is that crossover at 14 mm — the same habit that works in PLA is wrong in ABS at almost any useful size, and that's a property of the material rather than of anyone's printer.
- Calibrate once and the rest follows. Print a block with holes at nominal +0.1 through +0.5, try your actual pin or bearing in each, and note which fits. That gives the fixed term for your printer, filament and first-layer squish — twenty minutes, worth more than any table.
- Model the hole bigger and the peg smaller when the printed part has to mate with something bought — a bearing, a magnet, a standard bolt — where you don't get to move the other half.
- The first layer is the odd one out. Squish makes the bottom wider than the rest, so a hole starting on the bed is tighter than the same hole higher up. A chamfer on the bottom edge solves it geometrically for nothing.
- Small holes are worse than large ones. On the inside of a curve the extrusion is compressed rather than stretched, so a 3 mm hole can be 0.2 mm under where a 30 mm bore is nearer 0.1. If a small hole must be accurate, print it undersized and drill it.
How to use
- Enter the dimension the two parts share, not the size of the whole part.
- Pick the fit you actually want rather than the tightest one that might work.
- Check whether the feature is past the crossover for your filament.
- Measure your own per-surface error once with a test print.
Frequently asked questions
How much clearance does a 3D printed part need?
About 0.2 mm on the diameter for a press fit and 0.3 to 0.4 for a sliding one, up to roughly 30 mm in PLA. Past that, add twice the shrinkage: a 50 mm sliding fit in PLA wants nearer 0.6 mm and a 100 mm one nearer 0.9. The flat number is right for small features and increasingly short for large ones.
Where does the 0.2 mm clearance rule come from?
From four surfaces of extrusion error. A printed feature is off by about 0.05 mm per surface, and the error runs the same way on both halves of a fit — external features come out oversized, internal ones undersized. So a nominal 10 mm peg prints 10.10 and the matching hole 9.90, which is 0.20 mm of interference before any clearance is designed in. The rule is not arbitrary; it is that number.
Why do 3D printed holes come out too small?
Two reasons that push the same way. Extrusion overshoot puts material where the model says there is none, so an internal surface moves inward while an external one moves outward. And on the inside of a curve the extrusion is compressed rather than stretched, which makes small holes worse than large ones — a 3 mm hole can be 0.2 mm under where a 30 mm bore is nearer 0.1.
Does clearance scale with the size of the part?
Partly, and knowing which part scales is the whole trick. The extrusion error is fixed at about 0.2 mm on any diameter, while thermal shrinkage is proportional to the dimension. Below the size where those two are equal a flat rule works; above it the shrinkage term dominates and a flat rule is short. In PLA that crossover is 33 mm, in PETG 25, in ABS 14 and in nylon 8.
Why is ABS harder to get dimensionally right than PLA?
Because it shrinks more than twice as much, which moves the crossover from 33 mm down to 14. Below 14 mm the fixed error still dominates and ABS behaves like PLA; above it, shrinkage takes over and the habits that work in PLA are simply wrong. That single number is most of ABS being called dimensionally difficult, and it is a property of the material rather than of anyone printer.
What is the difference between a press fit and a slip fit?
A press fit is meant to need force and stay put, so you design for zero real gap after printing. A slip fit moves freely under hand pressure without slop, which wants about 0.1 mm of real gap. On a printer the difference between them is roughly 0.1 mm of designed clearance, which is close enough to the machine noise that a test print is worth more than a calculation.
Should I model the hole oversized instead of adding clearance?
Yes, when the printed part has to mate with something bought. Adding clearance works when you control both halves; when the other half is a bearing, a magnet or a standard bolt, you have to make the printed feature land on nominal — which means drawing the hole larger by the extrusion error plus the shrinkage, and the peg smaller by the same logic.
How do I calibrate clearance for my own printer?
Print a block with a row of holes at nominal plus 0.1, 0.2, 0.3, 0.4 and 0.5 mm, then try the actual pin or bearing in each and note which one fits. That single test gives you the fixed error for your machine, your filament and your first-layer squish, and every clearance after it scales from a measured number rather than a typical one. Twenty minutes, once.
Why is the bottom of my print wider than the rest?
Elephant foot — the first layer is squashed against the bed, so it spreads. It means a hole that starts on the build plate is tighter than the same hole higher up in the part, and a peg is fatter at its base. Slicers have an elephant foot compensation setting, and a small chamfer on the bottom edge of a fitting feature solves it geometrically for nothing.
Does clearance depend on the fit being a hole or a slot?
The arithmetic is the same but the count of surfaces is not. A round peg in a round hole has four surfaces of error across the diameter; a rectangular tab in a slot has four across the width and four across the thickness, so both dimensions need the clearance independently. Getting one right and forgetting the other is a common way to produce a part that almost fits.
Can I just print a test piece instead of calculating?
For a single fit, yes, and it will be more accurate. The value of the arithmetic is that it tells you how to carry that test result to a different size or a different filament — which the test on its own cannot do, because the fixed part transfers and the shrinkage part does not. Test to find your fixed error, then calculate everything else from it.
Does a bigger nozzle change the clearance I need?
It changes the fixed term, which is where nearly all the small-feature error lives. A wider extrusion overshoots more, so a 0.6 mm nozzle typically wants a little more clearance than a 0.4 for the same fit. It does not change the shrinkage term at all, so the crossover moves out slightly rather than the whole curve shifting.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.