3D Printing Tolerances and Clearances Guide

You model a peg and a hole at exactly the same size, print both, and the peg won't go in. Or you leave a generous gap and the parts rattle. Tolerance is the difference between the size you designed and the size you get, and clearance is the gap you add on purpose so parts fit. Both depend on the printer, the material and the settings.

This guide gives starting clearances for the common processes, explains why printed dimensions drift, and ends with a small test print that finds the right number for your own machine.

The resin and powder figures below come from the printer and service makers named, and the FDM figures are common rules of thumb. None are specifications for your machine. Printers, materials and slicer settings all change the result, so confirm them with a test print, check your service provider's design guide if you're ordering parts, and have anything safety-critical reviewed by an engineer who knows the application.

Starting clearances by process

FDM: as-printed accuracy is commonly around plus or minus 0.1 to 0.2 mm on a well-tuned machine. A clearance of about 0.2 to 0.3 mm per side is a common starting point for parts that should slide or fit loosely, and 0.1 to 0.15 mm for a snug fit.
Resin (SLA): the Formlabs Form 4 design specifications recommend a gap of at least 0.4 mm between parts and warn they may fuse below that. Formlabs lists accuracy of about 0.15% of the feature size (never better than 0.02 mm) for features up to 30 mm, loosening to 0.2% and 0.3% for larger ones. That is measured on a Form 4 with Grey Resin V5, so other resins and printers will differ.
Powder nylon, Formlabs SLS: the Formlabs Fuse 1 design specifications call for a minimum assembly clearance of 0.2 mm for small features (under 20 mm²) and 0.4 mm for larger ones. Formlabs' Formlabs SLS accuracy white paper reports a standard XY tolerance of ±0.5% or 0.3 mm, whichever is larger, for Nylon 12 on the Fuse series.
Powder nylon, HP Multi Jet Fusion: Xometry's HP Multi Jet Fusion design guide recommends a gap of at least 0.4 mm between mating parts, allowing ±0.2 mm of tolerance on each part, and 0.7 mm for print-in-place parts like hinges and ball joints, more for thick walls.
Press fits and tight fits: published minimums are for parts that must not fuse, so tight fits need a test. Don't guess. Print a test set at several sizes and choose from what you measure.

Per side, or total?

Clearance numbers are easy to misread. A 0.2 mm clearance per side means a hole 0.4 mm larger in diameter than the peg that goes in it. The resin and powder figures above are gaps between parts, so check how each source states its number. Many fit problems are just a per-side figure applied as a total, or the other way around.

Why printed parts miss their dimensions

Holes print small. On FDM, round holes usually come out smaller than modeled because the perimeter sags inward. Plan on adding material-removal clearance, or drill or ream holes that need to be exact.
Material shrinks as it cools. Different plastics shrink by different amounts, and large parts shrink more in absolute terms than small ones.
The first layers spread out. The bottom edge of an FDM part often flares slightly, an effect called elephant's foot. A small chamfer on the bottom edge stops it from affecting fit.
Orientation matters. Accuracy in the vertical direction depends on layer height, and horizontal accuracy depends on the nozzle and motion system. A part printed upright can differ from the same part printed flat.
Printers need calibration. Steps per millimetre, flow rate and nozzle wear all change the result, so a fit that worked last month may not work today.

Tolerances for common features

Sliding fit (lids, drawers, rails): start at the loose end of your range and tighten from there. A part that is too loose can be shimmed; a part that is too tight must be reprinted.
Snap fits: they depend on the flex of a thin arm as much as on clearance. See our guide on wall thickness for the thickness side of that problem.
Screw holes and inserts: follow the screw or insert maker's recommended hole size for your material, then test one.
Moving parts and hinges: leave enough clearance that the surfaces don't fuse or drag, especially in print-in-place designs, and expect to clean up the gaps.
Enclosure lids and seams: the DFM checklist for small enclosures covers lid fit, bosses and sealing in more detail.

Print a tolerance test

The reliable way to know your numbers is a small test piece printed in the material, orientation and settings of the real part. This is the same coupon approach we use in the 3D-printed adapter guide.

Model a block with a row of holes (or slots) stepping in size, for example 0.1 mm apart, around the nominal size you need.
Model a matching peg or tab at exactly the nominal size.
Print both, then try the peg in each hole and note which one is snug, which slides freely and which rattles.
Measure the peg and the best-fitting hole with calipers, and use the difference as your clearance for this printer and material.
Repeat if you change materials, nozzle, layer height or printer.

A quick checklist

Decide whether clearances are per side or total, and write it down.
Start with a process-appropriate clearance, then adjust from a test print.
Expect holes to print small and add a chamfer to bottom edges.
Test in the real material and orientation.
Leave adjustment room: parts that can be sanded or shimmed are more forgiving than ones that can't.

If your parts have to fit together in volume, or the fit is part of how the product works, the numbers above are a starting point. We design parts and assemblies for printing and for molding, and we'll tell you what your design needs. Tell us what you're building.