3D Printing Tolerances Explained: What Accuracy Can You Expect?

Updated March 2026 · 8 min read

FDM: ±0.3mm. SLA: ±0.1mm. SLS: ±0.15mm. Metal: ±0.05mm.

Those are the real-world numbers you should expect from each technology. If a shop promises tighter tolerances than that, they're either using specialized equipment or they don't know what they're talking about.

Understanding tolerance matters when parts need to fit together, mate with existing components, or meet dimensional specifications. Most prints don't need precision. But when you do need it, you need to know what's achievable and how to design for it.

What Tolerance Actually Means

Tolerance is how much a printed dimension can vary from the designed dimension. A hole designed at 10mm might measure 9.8-10.2mm if the tolerance is ±0.2mm.

Tighter tolerance = more dimensional accuracy = higher cost and slower production.

Most of the time, people worry about tolerance when they don't need to. A cosplay helmet that's 2mm bigger than designed? Nobody will notice. A bearing housing that's 0.2mm oversized? The bearing won't fit. Context matters.

FDM Tolerances: ±0.2-0.3mm Typical

Fused deposition modeling is the least precise common technology. You're melting plastic and extruding it through a nozzle—dimensional accuracy has limits.

What Causes FDM Variance

Layer height: 0.2mm layers mean every dimension in the Z-axis (print height) is rounded to the nearest 0.2mm. A 10.1mm tall feature prints as 10.2mm (51 layers).

Nozzle diameter: A 0.4mm nozzle can't produce features smaller than about 0.4mm. Walls, holes, and details will be slightly oversized or undersized depending on how the slicer paths the nozzle.

Material shrinkage: Plastic cools and shrinks. PLA shrinks about 0.3%, ABS shrinks 0.7-0.8%, nylon can shrink 1.5%. A 100mm part might end up 99.7mm (PLA) or 98.5mm (nylon).

Thermal expansion: The print is hot when it's made and cools to room temperature. Different areas cool at different rates, causing warping and dimensional changes.

Mechanical tolerances: Belts stretch, bearings have play, frames flex slightly. All of this adds up to positional error.

Real FDM Accuracy

Well-tuned FDM printer (Prusa, Bambu Lab, Ultimaker):

Average consumer FDM printer:

Budget FDM printer (poorly calibrated):

If you need ±0.2mm on FDM, ask the shop what printer they're using and how they calibrate. A well-maintained Prusa can hit it. A $200 printer from Amazon won't.

Designing for FDM Tolerances

Holes: Print 0.2-0.3mm undersized, then drill or ream to final dimension. A 10mm hole should be designed at 9.7mm, then drilled to 10mm.

Shafts: Print 0.2mm oversized, then sand or turn down to size. A 10mm shaft should be designed at 10.2mm.

Press fits: Add 0.3-0.5mm interference. If you need a 10mm shaft in a 10mm hole, design the shaft at 10.4mm. It'll press in tight but not crack the hole.

Snap fits: Add 0.5-0.8mm clearance for moving parts. A 10mm shaft that needs to rotate in a bearing should have a 10.8mm hole.

Thread tolerances: Don't print threads finer than M8. Smaller threads (M6, M4) are unreliable on FDM. Use threaded inserts instead.

SLA Tolerances: ±0.05-0.1mm Typical

Resin printing is much more precise than FDM because you're curing a liquid with a laser or projector. No nozzle diameter to worry about, minimal thermal shrinkage.

What Causes SLA Variance

Layer height: Most SLA printers use 0.05mm layers. Z-axis dimensions are quantized to 0.05mm increments.

Resin shrinkage: Resin shrinks about 0.2-0.5% as it cures. A 100mm part ends up 99.5-99.8mm.

Laser/projector resolution: Pixel size determines XY resolution. A 50-micron pixel means features smaller than 50 microns won't resolve correctly.

Over-curing: UV light bleeds slightly beyond the intended area, causing features to grow by 0.05-0.1mm. Small holes print smaller, thin walls print thicker.

Real SLA Accuracy

Desktop SLA printer (Elegoo, Anycubic):

Professional SLA printer (Formlabs Form 3+):

Industrial SLA (3D Systems, Stratasys):

For most applications, desktop SLA at ±0.1mm is more than adequate. If you need better, you're paying for industrial equipment.

Designing for SLA Tolerances

Holes: Print 0.1mm undersized, ream if precision is critical. SLA holes are more accurate than FDM but still benefit from post-processing.

Mating parts: Add 0.1-0.2mm clearance for slip fits, 0.05mm interference for press fits.

Fine threads: SLA can print M4 and M5 threads reliably. Smaller than that (M3, M2) is possible but fragile.

Thin walls: Minimum reliable wall thickness is 0.4-0.5mm. Thinner walls can print but are extremely fragile.

SLS Tolerances: ±0.15-0.2mm Typical

Selective laser sintering fuses nylon powder. It's more accurate than FDM but not as precise as SLA. The powder grain size and laser spot size limit resolution.

What Causes SLS Variance

Powder particle size: Nylon powder is 50-80 microns. Features smaller than that can't form correctly.

Laser spot size: Typically 0.2-0.4mm. This determines the minimum feature size and edge sharpness.

Material shrinkage: Nylon shrinks about 3-4% as it cools from sintering temperature (170-190°C) to room temp. A 100mm part becomes 96-97mm. Shops compensate by scaling models up pre-print, but there's still some variance.

Part packing: Multiple parts in the powder bed can affect cooling rates and shrinkage uniformly. Parts near the edge cool differently than parts in the center.

Real SLS Accuracy

Entry-level SLS (Formlabs Fuse 1+):

Industrial SLS (EOS, 3D Systems):

High-precision SLS (specialty equipment):

Most shops offering SLS run industrial equipment and can hit ±0.15mm consistently.

Designing for SLS Tolerances

Clearances: Add 0.3-0.5mm for slip fits, 0.2mm for press fits.

Threads: SLS prints excellent threads down to M4. The material is strong enough to handle threading force, unlike brittle SLA resin.

Snap fits: SLS nylon is flexible enough for living hinges and snap features. Add 0.5mm clearance for moving parts.

Thin walls: Minimum wall thickness is 0.7-1.0mm depending on part geometry. Thinner walls are possible but risk warping or breaking during depowdering.

Metal 3D Printing Tolerances: ±0.05-0.1mm

Metal additive manufacturing (DMLS, SLM, binder jetting) produces parts with the tightest tolerances of any 3D printing technology.

Real Metal Printing Accuracy

Standard metal AM:

High-precision metal AM:

Metal prints usually require machining for critical dimensions anyway. Holes, threads, and mating surfaces are printed undersized and then CNC-machined to final spec.

Metal printing is expensive ($5-20 per gram) and slow. Only used when traditional machining is impossible (internal lattices, complex geometries) or when material properties require it (titanium implants, Inconel turbine parts).

When Tolerance Doesn't Matter

Most 3D printing projects don't need precision. Here's when you shouldn't worry about it:

Display pieces: Cosplay armor, architectural models, decorative objects. If it looks right, dimensions don't matter.

Prototypes for form/fit testing: You're checking if the shape works, not building a production part. ±0.5mm is fine.

One-off custom parts: If you're not mating with an existing component, you can design everything to fit the printed dimensions rather than hitting a spec.

Large parts: On a 500mm part, ±0.3mm is 0.06% error. That's excellent. Tolerance anxiety is mostly a problem for small precision parts (under 50mm).

When Tolerance Matters A Lot

You need tight tolerances when:

Parts must fit together: Gears, bearings, mating housings. If two parts need to assemble, tolerances matter.

Mating with commercial components: Bearings, motors, fasteners, off-the-shelf parts. You can't change their dimensions, so your print must match.

Functional mechanical assemblies: If the part has to move, rotate, or transmit force, sloppy tolerances mean sloppy performance.

Replacement parts: If you're recreating a broken part, dimensions need to match the original within the tolerance that part was originally made to.

Medical/dental: Implants, aligners, surgical guides. These need to fit biological anatomy precisely.

How to Communicate Tolerance Requirements

When you send a file to a printing shop, include tolerance callouts if they matter:

General tolerance: "All dimensions ±0.2mm unless noted."

Critical dimensions: Use dimension lines and tolerance callouts in your CAD drawing. "10.0mm ±0.05mm" tells the shop that hole needs to be tight.

Functional requirements: "Shaft must rotate freely in bearing." The shop knows to add clearance even if you didn't specify exact tolerance.

Mating parts: "This part mates with [include STL of the other part]." Shops can test-fit if they have both files.

Good shops will ask questions if your tolerances are tighter than the technology can achieve. If they just say "sure, we can do that" without asking follow-up questions, be skeptical.

Testing Tolerance Before Full Production

Smart approach: print a test piece first.

Tolerance test part: Design a small part with critical features (holes, shafts, threads, mating surfaces). Print it, measure it, test-fit it. If it works, proceed with the full print. If not, adjust dimensions and try again.

Cost: $10-30 for a test piece. Saves you $100-500 by catching tolerance issues before printing the full part.

Most experienced shops will recommend this if you're printing functional parts for the first time.

Measuring Your Prints

You can't manage what you don't measure. To verify tolerance:

Calipers: Digital calipers ($20-40) measure external dimensions to 0.01mm resolution. Good enough for most FDM and SLA work.

Micrometers: For ±0.05mm or tighter, you need a micrometer ($50-150). Measures to 0.001mm resolution.

Pin gauges: For checking hole diameters accurately. A set of pins in 0.01mm increments costs $50-100.

CMM (Coordinate Measuring Machine): Industrial inspection tool. Measures 3D geometry to ±0.005mm. Only necessary for aerospace/medical parts. Service costs $100-300 per part.

For most work, calipers are sufficient. If you're doing functional engineering work, invest in a micrometer.

Fixing Tolerance Problems

If your part doesn't meet tolerance:

Holes too small? Drill or ream them. Easier than reprinting.

Shafts too big? Sand, file, or turn them down on a lathe.

Press fit too tight? Sand the male part or drill out the female part slightly.

Snap fit too loose? Add a shim, use adhesive, or redesign with tighter clearance and reprint.

Threads don't work? Chase them with a tap (internal threads) or die (external threads). Or use threaded inserts instead.

Most tolerance issues can be fixed with $20 in hand tools and 20 minutes of work. It's almost always faster than waiting for a reprint.

Material-Specific Tolerance Notes

PLA (FDM): Minimal shrinkage, easy to hit ±0.3mm. But it's brittle—tight tolerances can cause parts to crack during assembly.

ABS (FDM): Warps and shrinks significantly. Hard to achieve good tolerance on parts larger than 100mm. Use PETG instead.

PETG (FDM): Slight shrinkage, very predictable. Best FDM material for parts requiring tolerance.

Nylon (FDM): Absorbs moisture from air, which changes dimensions. Print it, measure it immediately, seal it in a bag. Dimensions will change if left exposed.

Standard resin (SLA): Shrinks slightly, brittle. Good tolerance but fragile at stress points.

Castable resin (SLA): Designed to burn out cleanly, not for dimensional accuracy. Expect ±0.2mm or worse.

PA12 (SLS): Predictable shrinkage, good tolerance, durable. Best all-around material for functional parts requiring precision.

The Calibration Factor

Tolerance isn't just about the technology—it's about how well the machine is maintained and calibrated.

A perfectly calibrated Prusa MK4 can outperform a poorly maintained industrial machine. A shop that runs monthly calibration checks, replaces worn parts, and uses quality materials will deliver better tolerance than one that doesn't.

Questions to ask a shop:

If they can't answer those questions, they're probably not set up for precision work.

The Honest Truth About Tolerance

Most prints don't need tight tolerance. The people who obsess over ±0.05mm are usually overthinking it.

Design for the tolerance you can get, not the tolerance you wish you had. Add clearance. Use fasteners instead of press fits. Plan for post-processing.

When you truly need precision—bearings, gears, mating assemblies—then pay for SLA or SLS, specify your tolerances clearly, and budget for test prints.

But if you're printing a phone case, a helmet, or a prototype, stop worrying about 0.1mm and just print it. It'll be fine.

Need precision parts? Find a shop that offers the technology and calibration standards your project requires.

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find3dprinting.com Editorial Team

We've reviewed 500+ 3D printing services across the US to help you find the right shop for your project.