FDM Tolerances by Machine and Formulation

Why a tolerance number needs its formulation

Published FDM tolerance figures use at least three different formulations, a percent of the part's dimension, a step per inch of length, and a fixed distance in millimeters, and these are not interchangeable. A tolerance number quoted without its formulation and its machine class means nothing on its own.

Protolabs Network states FDM tolerance as a percent of the dimension being measured. Xometry states it as one layer thickness for the first inch of a dimension, then a fixed step for every inch after that. Stratasys states it as a fixed distance in millimeters, or a percent of the dimension, whichever is greater. Converting between these needs the actual size of the feature being toleranced, not just the published number.

What tolerance can FDM hold?

Across the sources checked here, published FDM tolerance ranges from about 0.1 mm on a well assembled desktop printer to a floor of 0.5 mm at an industrial bureau's loosest published tier. Every number comes from that source's own machines and test methods, not a promise about your specific part.

Is 0.1 mm a tight tolerance?

0.1 mm sits at the tight end of what is published for FDM: Prusa lists 0.1 mm on Z for a well assembled desktop printer, and Stratasys's Fortus 450mc spec floors at 0.127 mm. Nothing published in the sources checked here claims a tighter number for FDM.

What is the tightest tolerance 3D printer?

Between the two Stratasys machines with published specs here, the Fortus 450mc floors tighter at 0.127 mm or 0.0015 mm per mm, compared with the F370's 0.200 mm or 0.002 mm per mm. Stratasys's own footnote calls this a statistical yield figure, not a guarantee on any single part.

"Accuracy is geometry-dependent. Achievable accuracy specification derived from statistical data at 95% dimensional yield. Z part accuracy includes an additional tolerance of -0.000/+slice height." That is Stratasys's own F370 footnote: an OEM stating its own spec is a yield statistic across many geometries, not a promise about the one part you send it, and that the Z axis always prints from exact to one layer oversize.

How does Xometry's per inch tolerance work?

Xometry's standards page states FDM tolerance as one full layer thickness for the first inch of a dimension, then 0.002 in for every inch after that. Layer thickness itself depends on the machine, from 0.008 in on a desktop machine up to 0.013 in on a Fortus 900.

This means Xometry's tolerance grows with the size of the part being measured, unlike a flat mm figure or a flat percent figure. A one inch feature and a ten inch feature on the same machine do not carry the same absolute tolerance in this formulation.

What tolerance do we quote to?

FDM parts typically hold about plus or minus 0.5 percent, with a floor near plus or minus 0.5 mm. We do not certify a tolerance number on a quote.

No CMM, no dimensional reports, no PPAP, no first article inspection. If your part needs a measured report to be accepted, we are not the right supplier.