3D print tolerance calculator: clearance for every kind of fit

The formula

C = 2 × c

enlarge the hole:   hole = D + C        pin = D
shrink the pin:     hole = D            pin = D − C
split it:           hole = D + C ÷ 2    pin = D − C ÷ 2

then:  hole + how much your holes print small
       pin − how much your pins print large

• D is the nominal size both parts share: the pin’s diameter, or the width of a tongue, dovetail or box wall.
• c is the clearance per side, the gap at one face. C is the total clearance, hole minus pin, measured across the diameter or the width.

A guide that says “0.2 mm” can mean either, and the two differ by a factor of two. Every value on this page and in the calculator is per side, paired with its total.

How much tolerance do you need for 3D printing?

On a filament (FDM) printer, model 0.1 mm of clearance per side for a snug fit, 0.2 to 0.3 mm for sliding parts, and 0.3 to 0.4 mm for a print-in-place hinge. Across the diameter that is 0.2 mm, 0.4 to 0.6 mm and 0.6 to 0.8 mm. Press fits run from slight interference to 0.2 mm per side.

Fit	Use it for	Per side	Total	Inches, per side / total	Published range, per side
Press	a pin that stays put without glue	−0.05 mm	−0.10 mm	−0.0020 / −0.0039 in	−0.15 to −0.05 mm (QIDI)
Snug	locating pegs, no wobble	0.10 mm	0.20 mm	0.0039 / 0.0079 in	0.10 to 0.15 mm (UAL lab, Bambu H2D Pro)
Turning pin	a dowel, pin or axle that must rotate	0.20 mm	0.40 mm	0.0079 / 0.0157 in	0.15 to 0.25 mm (QIDI)
Sliding (slip fit)	dovetails, rails, drawers	0.25 mm	0.50 mm	0.0098 / 0.0197 in	0.20 to 0.30 mm (QIDI, Sovol)
Snap or friction lid	a box lid or cap that stays on	0.20 mm	0.40 mm	0.0079 / 0.0157 in	0.20 to 0.25 mm (QIDI)
Loose	a drop-in lid, tray or cover	0.40 mm	0.80 mm	0.0157 / 0.0315 in	0.30 to 0.50 mm (QIDI)
Print-in-place hinge	hinges and joints printed assembled	0.35 mm	0.70 mm	0.0138 / 0.0276 in	0.30 to 0.40 mm (QIDI)

The per-side column is the calculator’s default for each fit, mostly the middle of the published range. The press fit takes QIDI’s lightest interference, and the snug fit and the lid take the tight end of their ranges so the part holds. QIDI’s values assume a 0.4 mm nozzle, 0.2 mm layers and PLA or PETG on a calibrated printer. For ABS and ASA, add 0.05 to 0.10 mm per side; for unfilled nylon, add 0.10 to 0.20 mm.

Your printer matters as much as the fit. The Creative Computing Institute lab at University of the Arts London (the UAL lab in the tables) publishes 0.15 to 0.2 mm per side for hinges and sliding parts on its Bambu H2D Pro machines, and 0.3 mm or more on its UltiMaker S7s. Treat the table as a starting value and correct it with a test print.

Worked example: a 6 mm dowel that turns

These are the calculator’s defaults.

1. Fit: turning pin, 0.20 mm per side, so 0.40 mm total.
2. The steel dowel can’t change size, so the hole takes the clearance: 6 + 0.40 = 6.40 mm (0.2520 in). The dowel stays at 6 mm (0.2362 in).
3. If a test print showed your holes coming out 0.10 mm small, enter 0.10 in “Holes print smaller by” and model the hole at 6.50 mm. The fit is still 0.40 mm; the extra 0.10 mm offsets the printer’s error.

Worked example: a 1/4 in dowel, in inches

Pick “Inches” as the unit, type 0.25 and choose the snug fit. Its 0.10 mm per side is 0.0039 in, or 0.0079 in total. Model the hole at 0.2579 in (6.55 mm). The clearance field stays in millimeters, and every result shows both units.

What clearance should a hinge, dowel or dovetail joint have?

A print-in-place hinge needs 0.3 to 0.4 mm per side, or 0.6 to 0.8 mm across the pin. A dowel or pin fitted after printing needs 0.15 to 0.25 mm per side to turn freely. A sliding dovetail needs 0.2 to 0.3 mm on each mating face, and a snap or friction box lid 0.2 to 0.25 mm.

Hinges

QIDI sets 0.30 to 0.40 mm per side because the gap has to exceed about one extrusion width in XY, or the walls weld together. Sovol lists “about 0.3 to 0.4 mm total” for hinges, half of QIDI’s figure once split over two sides. If a hinge fuses at Sovol’s value, check that difference first.

For a 5 mm hinge pin, keep the pin at 5 mm and model the barrel’s bore at 5.70 mm. Between the knuckles the gap runs in Z. Stratasys asks for at least twice the layer height there, and QIDI for a whole number of layers: 0.4 mm at 0.2 mm layers. A hinge assembled after printing is a turning pin, so pick that fit.

Dowels, pins and shafts

• A pin that turns: 0.15 to 0.25 mm per side (QIDI). For a metal dowel, put the clearance on the hole.
• A pin that stays put: published press fits run from 0.15 mm of interference to 0.2 mm of clearance per side, 0.7 mm apart on the diameter (see the source table below). Print a short section of the boss and the hole before the full part.
• A printed shaft in a bought bushing or bearing bore: pick “The pin” so the hole stays at the bushing’s size and the shaft shrinks.

Holes for screws and threads follow their own tables: use the screw hole size calculator and the thread calculator.

Dovetails and sliding joints

QIDI and Sovol both give 0.20 to 0.30 mm per side for sliding parts. Below 0.20 mm, QIDI adds, friction jumps because layer ridges act as small interferences.

On a dovetail, offset each angled flank by the per-side value. Widening the slot by the total instead leaves a smaller gap on the flanks. At a flank 30° from vertical, the gap is cos 30° (87%) of the value you typed.

Print the slot and the tongue in the same orientation, with the sliding direction along the layer lines. If a slide still binds, put the mating faces in the X/Y plane, which Stratasys rates as the most accurate.

Box lids

A lid that snaps or holds on a box needs 0.20 to 0.25 mm per side, and a lid or tray that drops in with no latch needs 0.30 to 0.50 mm (QIDI). For a snap lid on a box 80 mm wide outside, model the lid’s inside at 80.40 mm, then do the same for the length.

A lid that sits over the box is the hole, and the box wall is the pin. A lid that plugs into the box opening is the pin: pick “The pin” to shrink the lid and keep the opening at size.

Published FDM clearances, source by source

Here is what each source publishes, and whether its figure is per side or total.

Source	Fit	Clearance as published	Per side or total
QIDI	Hinge printed in place	0.30 to 0.40 mm (0.60 to 0.80 mm on the diameter)	per side, with a total column
QIDI	Pin fitted after printing, turning	0.15 to 0.25 mm (0.30 to 0.50 mm on the diameter)	per side
QIDI	Sliding dovetail or rail	0.20 to 0.30 mm	per side
QIDI	Lid that snaps or holds on a box	0.20 to 0.25 mm (0.40 to 0.50 mm across)	per side
QIDI	Drop-in lid or tray	0.30 to 0.50 mm	per side
QIDI	Press-fit pin	−0.05 to −0.15 mm (interference)	per side
Sovol	Press fit	0.05 to 0.15 mm	per side
Sovol	Sliding fit (lids, drawers)	0.2 to 0.3 mm	per side
Sovol	Moving parts, hinges	about 0.3 to 0.4 mm	total
UAL lab, Bambu H2D Pro	Press / alignment peg / hinge or sliding / free movement	0 to 0.05 / 0.1 to 0.15 / 0.15 to 0.2 / 0.2 mm or more	per side
UAL lab, UltiMaker S7	Press / alignment peg / hinge or sliding / free movement	0.2 / 0.2 / 0.3 or more / 0.4 mm or more	per side
Prusa	Movable parts	at least 0.3 mm	not stated
Xometry Pro	Sliding fit	0.2 to 0.3 mm	not stated
Stratasys	Any assembly, printers without a stated accuracy	at least 0.51 mm (0.020 in) in X/Y, twice the layer height in Z	a gap between parts; says to use “radial or diametrical” as appropriate
Fathom	Assemblies, 0.127 mm layers	0.5 mm	not stated
OrcaSlicer tolerance test	Six test holes	0, 0.05, 0.1, 0.2, 0.3 and 0.4 mm	not stated

The UAL lab spells out its convention: a 10 mm peg with 0.1 mm tolerance gets a 10.2 mm hole. When a source does not say, read the figure both ways before you model: a per-side value read as total gives a fit half as loose as intended. Stratasys’s 0.51 mm is for its Dimension, uPrint and Mojo printers.

Why FDM needs more clearance than a machined fit

A printed part misses its size by more than a machined fit’s whole tolerance. In the ISO 286 tables, an H7 hole of 10 mm may be 0 to 0.015 mm oversize and a g6 shaft 0.005 to 0.014 mm undersize. That H7/g6 pairing, ISO’s sliding fit, leaves 0.005 to 0.029 mm of total clearance. Printers are rated far coarser:

• Protolabs Network gives desktop FDM a dimensional accuracy of ±0.5%, with a lower limit of ±0.5 mm.
• Prusa states its printers are accurate to at least 0.2 mm.
• Stratasys rates its Fortus 380mc and 450mc at ±0.127 mm (±0.005 in), or ±0.0015 mm per mm.

Both parts carry that error, and on a fit it runs one way. Holes print small, with about four times the error of outside dimensions, while outside walls print large from extrusion width and first-layer squish (QIDI). The clearance absorbs both, which is why a 0.50 mm sliding clearance is 17 times the loosest H7/g6 fit at 10 mm.

When the fit is still wrong

• Every hole is tight: check flow first with the flow rate calculator, since over-extrusion closes every gap. Then print a hole and a pin at a round size and measure both with calipers. Enter the differences in the two printer correction fields, or fix every model at once with the slicer offset from the hole compensation calculator.
• You want a measured value: OrcaSlicer’s Orca Tolerance Test prints six hexagonal holes from 0 to 0.4 mm, checked with a 6 mm Allen key or the printed tester. Right-click the plate in Prepare mode and choose “Add Handy Model”. QIDI’s method works in any slicer: print five copies of your joint at 0.10 to 0.50 mm and keep the smallest gap that moves freely.
• Tight only at the bottom: that is elephant’s foot, the first layers squashed wider than the rest. Set elephant foot compensation in the slicer at 0.15 to 0.25 mm, or chamfer the bottom edge 0.4 mm × 45° (both QIDI).
• The whole part is off, not just the fit: that is shrinkage or scale. Use the shrinkage calculator for material shrink and the scale calculator to resize a model. The dimensional accuracy guide puts the three corrections in order.