“How accurate is 3D printing?” is one of the first questions we get from engineers and product developers, and the honest answer is: it depends on the technology, the geometry, and the material. With the right process, a printed part can hold tolerances tight enough for snap fits, press-fit inserts, and assemblies that mate with molded or machined components. After 22+ years of printing parts in our Glendale shop, here is how we explain 3D printing accuracy to customers, with realistic tolerance ranges for each technology we run.
3D Printing Accuracy vs. Resolution: They Are Not the Same Thing
Resolution is how small a feature a printer can produce, usually expressed as layer height or minimum feature size. Accuracy is how close the finished part is to the CAD model. A printer with a 25-micron layer height can still produce a part that is 0.3 mm oversize if the material shrinks or warps. When you are checking whether a part will fit, accuracy and repeatability are the numbers that matter, and those come from the whole process: machine calibration, material behavior, part orientation, support strategy, and post-processing.
Tolerances are usually quoted as “plus or minus X mm or Y percent of the dimension, whichever is greater,” because part of the error is fixed machine positioning and part scales with size through shrinkage.
Typical 3D Printing Tolerances by Technology
The ranges below are what we consider realistic for well-designed parts under normal shop conditions. Small, compact geometry lands at the tighter end; large, thin, or flat parts drift toward the looser end.
FDM (fused deposition modeling)
Expect roughly ±0.2 to ±0.5 mm on parts up to about 100 mm, with the percentage term growing on larger prints. FDM is the least accurate of the common technologies because extruded plastic shrinks as it cools, and materials like ABS and nylon shrink more than PLA or PETG. Holes tend to print slightly undersize. FDM is a great choice for fixtures, enclosures, and functional prototypes where a reamer can finish a critical hole.
SLA (stereolithography)
Resin printing is one of the most accurate options for small and medium parts, typically ±0.1 to ±0.2 mm, with excellent surface finish and fine feature reproduction. The main variables are resin shrinkage during UV cure and distortion from supports on thin, unsupported spans. SLA is our go-to for master patterns, cosmetic prototypes, and parts with fine text or detail.
SLS (selective laser sintering)
Nylon SLS parts generally hold ±0.2 to ±0.3 mm, or about ±0.3 percent on larger dimensions. Because the unsintered powder supports the part, there are no support marks, and geometry can be complex. Large flat surfaces can bow slightly as the build cools, so we orient parts to minimize that. SLS is a strong option for living hinges, snap fits, and end-use nylon parts.
MJF (multi jet fusion)
MJF is similar to SLS in accuracy, usually ±0.2 to ±0.3 mm, with slightly better consistency across a full build because of how the process fuses each layer. The PA12 material suits production runs of small brackets, clips, and housings, with a matte, slightly textured surface unless finished.
DMLS (metal 3D printing)
Direct metal laser sintering typically holds ±0.1 to ±0.2 mm on small features, but residual stress and thermal distortion are the real challenge on larger metal parts. Critical surfaces, threads, and bearing bores are almost always finish-machined after printing. We design machining stock onto those features and treat the print as a near-net-shape blank.
What Affects 3D Printing Accuracy on Your Part
Within a single technology, these factors move a part toward the tight or loose end of the range:
Part size and wall thickness. Shrinkage is proportional, so a 200 mm part deviates more than a 20 mm part. Thin walls flex and warp.
Orientation. Dimensions along the Z axis are governed by layer height and are often the least accurate. Holes print rounder when their axis is vertical.
Holes and inside features. Almost every process prints holes slightly small. We recommend designing in a small offset or planning to ream critical holes.
Post-processing. Sanding, vapor smoothing, dyeing, and heat treatment all change dimensions slightly.
Assembly fits. For mating parts, a clearance of about 0.2 to 0.3 mm per side is a safe starting point for SLS, MJF, and FDM; SLA can go tighter.
How to Specify Tolerances for a 3D-Printed Part
You do not need to tolerance every dimension. Call out the few that matter: mating features, hole sizes for inserts or fasteners, and any surface that seats against another part. Tell us which features are critical and we will pick the technology, orientation, and finishing plan to hit them, or flag the ones that need secondary machining. A drawing with GD&T is ideal; a short note about how the part is used is usually enough.
For parts that must be verified, we can 3D scan the finished print and compare it to the CAD model to produce a deviation map before you commit to a larger batch.
Get Accurate 3D-Printed Parts in Los Angeles
eCadCam runs FDM, SLA, SLS, MJF, and DMLS in Glendale, so we match your part to the process that actually meets its tolerance requirements. Learn more about our 3D printing services, or send us your file and a note about the critical dimensions to request a quote. You can also reach us at 213.489.1173 or visit the shop at 4212 San Fernando Rd, Glendale, CA 91204.