What tolerance can a 3D printing service hold?

A tuned FDM service typically holds about plus or minus 0.5 percent of a size, with a floor near plus or minus 0.5 mm on small features. Those are typical numbers, not a guarantee on every feature. Long parts and wide flat parts drift the most. If one measurement is critical, call it out in your order notes.

How much clearance should I add between 3D printed parts?

Add 0.10 to 0.15 mm per side for a press fit, 0.20 to 0.25 mm for a snug hand fit, and 0.30 to 0.40 mm for a free sliding fit. Clearance is per side, so a hole for a 10 mm pin at a snug fit should be drawn near 10.4 mm. Print one test pair before you order a batch.

Why do holes in 3D prints come out too small?

Holes print 0.1 to 0.4 mm under size for two reasons. The slicer turns the circle into short straight lines that sit inside the true curve, and the plastic pulls inward a little as it cools. Draw holes 0.2 to 0.4 mm bigger than whatever has to pass through them.

Is FDM accurate enough for functional end-use parts?

Yes, for most functional parts. Brackets, enclosures, jigs, fixtures, and guards all live comfortably inside a plus or minus 0.5 percent range once you design clearance in. The parts that struggle are the ones with a press fit on a bearing or a shaft. Those work better with a reamed hole or a metal insert.

Which 3D printing material holds size best?

PLA holds the drawn size best, because it shrinks the least as it cools. PETG runs close behind and is our default for working parts, since it also handles heat to about 73 C. ABS shrinks the most and can pull wide flat parts out of square, so we steer big plates toward PETG.

How do I get a tighter tolerance than FDM gives?

Move the tight feature off the printer. Print a hole undersize and ream it, press in a steel bushing or a heat-set insert, or design a slot and a set screw so the joint can be adjusted. Another option is to keep the tolerance on a flat face you can sand rather than inside a deep bore.

Does part size change the tolerance?

Yes. The drift is a percentage of the size, so a longer part drifts more in absolute mm. A 200 mm rail can move about 1 mm end to end. Small parts are ruled by the floor instead, near plus or minus 0.5 mm, because half a percent of 10 mm is far too small to hold.

3D printing tolerances: the real FDM numbers, in mm

By the 3D Printer on Demand team · Updated July 2026

A 3D printing tolerance is how far a finished part can drift from the size you drew. For FDM, plan on about plus or minus 0.5 percent of the size. Small parts hit a floor near plus or minus 0.5 mm, because a percent of a small number is tiny. Those are typical numbers, not a promise on every feature. Tolerance is the drift the process leaves. Clearance is the gap you draw on purpose so the drift stops mattering. Design the gap and the fit works.

What tolerance can FDM hold?

Plan on about plus or minus 0.5 percent of the size, and no tighter than about plus or minus 0.5 mm. That is the typical range for a tuned FDM machine. A 200 mm rail can land near 199 mm or 201 mm. A 12 mm boss is ruled by the floor, not by the percent.

Treat that as a planning number, not a promise. Most features land well inside it. A few do not. Long thin parts and wide flat parts drift the most, because plastic pulls in as it cools.

The number also changes by feature. Height behaves nothing like width. A hole behaves nothing like an outside wall. Here is what to expect from each one.

Typical FDM tolerance by feature type, with the design move that handles each one.
Feature	Typical drift	What to do about it
Outside length or width	About 0.5 percent, no tighter than about 0.5 mm	Add clearance instead of chasing the exact number
Height, the Z axis	Lands in steps of the 0.20 mm layer height	Round heights to a multiple of 0.20 mm
Printed hole	Comes out 0.1 to 0.4 mm under size	Draw the hole 0.2 to 0.4 mm oversize
Wall thickness	Rounds to whole passes of a 0.4 mm nozzle	Size walls in steps of 0.4 mm, 1.2 mm and up
Flat face over 150 mm	Corners can lift or bow as the part cools	Add ribs, split the part, or pick PETG over ABS

Tolerance, clearance, and fit are three different things

Buyers mix these three words up all the time, and it costs them a batch. Tolerance is the drift the machine leaves behind. You do not control it. Clearance is the gap you draw between two parts on purpose. You control that one fully. Fit is how the pair feels once they meet.

The order matters. First you learn the drift. Then you draw a gap bigger than the drift. Then you get the fit you wanted. Skip the middle step and the part is a coin flip.

Our 3D printing glossary defines these and the rest of the terms you will meet on a quote.

How much clearance to design in

Use these gaps as your starting point. They are per side, and they are where most working parts land. Print one pair first and adjust from there.

Clearance per side for common FDM fits, with what each fit feels like.
Fit	Gap per side	How it feels	Use it for
Press fit	0.10 to 0.15 mm	Needs a tap or a clamp	Pins, dowels, parts that go in once
Snug fit	0.20 to 0.25 mm	Goes together by hand	Lids, covers, keyed blocks
Sliding fit	0.30 to 0.40 mm	Slides with light drag	Rails, trays, moving arms
Free fit	0.50 mm and up	Loose, no drag at all	Bolt holes, cable pass-throughs

Clearance is per side, not total. A 10 mm pin with a snug fit needs a 10.4 mm hole, not a 10.2 mm hole.
Split the gap when both parts are printed. Shave the pin a little and open the hole a little.
Warm parts grow. If the joint runs hot, go up one fit class.
Test with a small coupon, not the whole part. A short test print beats a long reprint.

Why holes print smaller than you drew them

Holes in FDM parts almost always come out 0.1 to 0.4 mm under size. Two things cause it. The slicer turns your circle into short straight lines that sit inside the true curve. Melted plastic also pulls inward a touch as it cools.

The fix is simple. Draw the hole 0.2 to 0.4 mm bigger than the pin or screw that goes through it. For screws that cut their own thread into plastic, draw the hole at the screw's minor size instead.

Bolt holes are the easy case. Give them a free fit and move on. Bearing seats and shaft holes are the hard case, and those are the ones to call out when you order.

Print orientation changes what you can hold

An FDM part is not the same in all three directions. It is built from stacked layers, so the way it sits on the bed changes both size and strength.

Height lands in layer steps. Our standard layer is 0.20 mm, so a 5.1 mm wall prints as 5.0 mm or 5.2 mm. Round your heights to the layer and Z stops surprising you.

Holes that stand up through the layers stay round. Holes that lie sideways sag a little at the top as they bridge open air, so they end up shaped like a teardrop. Turn the part so the fussy holes stand up, or draw the sideways ones as a teardrop on purpose.

Layer lines are also the weak line. A part pulled apart along the layers is weaker than the same part pulled across them. Tell us which way the load runs and we aim the layers to take it. There is more on this in our design for 3D printing guide.

Does the material change the tolerance?

A little. Shrink is the reason. Every plastic pulls in as it cools, and the ones that pull hardest fight you the most on wide flat parts.

The numbers below are the ones that decide the job. Strength is tensile strength. Heat is the point where the part starts to lose its shape under load.

How each material we print behaves on size, next to its strength and heat numbers.
Material	Strength	Holds shape to	How it behaves on size
PLA	50 MPa	57 C	Shrinks the least, so it holds the drawn size best
PETG	50 MPa	73 C	Close to PLA, can leave fine strings in holes and slots
ABS	40 MPa	98 C	Shrinks the most, so wide flat parts pull out of square
PA-CF	80 MPa	140 C	Very stiff and stays put, but nylon has to be dried first
TPU	35 MPa	80 C	Bends, so the measured size shifts with how you hold it

PLA is the most accurate of the five, but it softens at 57 C and cracks under a sharp hit.
PETG is our default for working parts. It gives up almost nothing on size.
ABS is the one to watch on big flat plates. Ribs and a split part both help.
PA-CF is the pick when the part has to stay stiff under load, not because it is more accurate.

What to do when you need a tighter fit than FDM holds

FDM has a floor, and some parts need to go under it. You do not have to give up on printing. You design around the limit instead.

These five moves cover almost every tight-fit job we see.

Machine the one feature that matters. Print the hole small, then drill or ream it. A metal tool holds size far better than melted plastic.
Let a metal part carry the tolerance. A steel bushing, a heat-set insert, or a bearing brings its own size with it. The plastic just holds it.
Design the joint so it can adjust. A slot instead of a hole, a set screw, or a thin shim lets you dial the fit in after the print.
Order one part first, not the batch. A single sample tells you the truth about the fit. Then you order the run with the gap corrected.
Move the tolerance to a face you can sand. A flat mating face cleans up in seconds. A blind bore does not.

Tell us which measurement matters

Every upload to our instant quote runs a printability check. It measures the part, flags walls that look too thin, and catches meshes with holes in them. The flags show up next to your price before you spend anything.

If one measurement on the part really has to land, put it in the notes. Our team reads flagged parts and gets back to you within four business hours. That is the moment to say a bore is a bearing seat, or that two parts have to slide.

Our 7 design checks page covers the rest of the pre-upload list. Parts ship in 2 to 5 days, made in the USA. Pricing is one flat price per part, and it drops as the quantity goes up. See the tiers on our pricing page.

Quick takeaways

Typical FDM tolerance is about plus or minus 0.5 percent, with a floor near plus or minus 0.5 mm. Treat it as typical, not guaranteed.
Clearance is per side. Press fit 0.10 to 0.15 mm, snug fit 0.20 to 0.25 mm, sliding fit 0.30 to 0.40 mm.
Draw holes 0.2 to 0.4 mm oversize, because FDM holes always come out small.
Round heights to the 0.20 mm layer, and stand fussy holes up so they print round.
For a fit tighter than FDM holds, ream the hole, drop in a metal insert, or design an adjustment into the joint.
Flag the measurement that matters in your order notes and our team reviews it within four business hours.

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Common questions

What tolerance can a 3D printing service hold?: A tuned FDM service typically holds about plus or minus 0.5 percent of a size, with a floor near plus or minus 0.5 mm on small features. Those are typical numbers, not a guarantee on every feature. Long parts and wide flat parts drift the most. If one measurement is critical, call it out in your order notes.
How much clearance should I add between 3D printed parts?: Add 0.10 to 0.15 mm per side for a press fit, 0.20 to 0.25 mm for a snug hand fit, and 0.30 to 0.40 mm for a free sliding fit. Clearance is per side, so a hole for a 10 mm pin at a snug fit should be drawn near 10.4 mm. Print one test pair before you order a batch.
Why do holes in 3D prints come out too small?: Holes print 0.1 to 0.4 mm under size for two reasons. The slicer turns the circle into short straight lines that sit inside the true curve, and the plastic pulls inward a little as it cools. Draw holes 0.2 to 0.4 mm bigger than whatever has to pass through them.
Is FDM accurate enough for functional end-use parts?: Yes, for most functional parts. Brackets, enclosures, jigs, fixtures, and guards all live comfortably inside a plus or minus 0.5 percent range once you design clearance in. The parts that struggle are the ones with a press fit on a bearing or a shaft. Those work better with a reamed hole or a metal insert.
Which 3D printing material holds size best?: PLA holds the drawn size best, because it shrinks the least as it cools. PETG runs close behind and is our default for working parts, since it also handles heat to about 73 C. ABS shrinks the most and can pull wide flat parts out of square, so we steer big plates toward PETG.
How do I get a tighter tolerance than FDM gives?: Move the tight feature off the printer. Print a hole undersize and ream it, press in a steel bushing or a heat-set insert, or design a slot and a set screw so the joint can be adjusted. Another option is to keep the tolerance on a flat face you can sand rather than inside a deep bore.
Does part size change the tolerance?: Yes. The drift is a percentage of the size, so a longer part drifts more in absolute mm. A 200 mm rail can move about 1 mm end to end. Small parts are ruled by the floor instead, near plus or minus 0.5 mm, because half a percent of 10 mm is far too small to hold.