1.75 mm vs 2.85 mm Filament: Which Does Your Printer Use?

Who this guide is for

This guide is for anyone about to buy filament who isn't sure which size their printer takes, or who has seen "3 mm" on a listing and wondered whether it's a third option. It covers the two sizes, why a printer is built for only one, where makers publish the size, how much diameter variation filament makers say their spools have, and the slicer setting that has to match. It doesn't compare materials. For that, start with the filament finder.

PLA: what to check before you buy a spool ↗

Is 3 mm filament the same as 2.85 mm?

Prusa's knowledge base puts it plainly: "3D printers mainly use two different diameters (thickness) of filament: 2.85 mm (commonly called 3 mm) and 1.75 mm. Worldwide, the 1.75mm version is more common." Simplify3D's print quality guide agrees that "the most common values for the filament diameter are 1.75mm and 2.85mm."

So a spool sold as "3 mm" belongs with the 2.85 mm printers, not to a third size. When you shop, the number on the label that matters is whichever of the two your printer's maker lists.

Can a printer use both 1.75 mm and 2.85 mm filament?

Printer makers specify one diameter for the whole printer, and the parts that handle filament are sold by diameter:

• Prusa. "All of our Original Prusa FFF-printers are configured for 1.75mm filament."
• UltiMaker. Its S5 page lists a compatible filament diameter of 2.85 mm, "the filament diameter that achieves optimal results on UltiMaker S series 3D printers." Its UltiMaker 3 support article says the printer "is only set up for 2.85 mm materials."
• Bambu Lab. The spec tables for the A1 and the X1 series list a filament diameter of 1.75 mm, and so does the spec table for the AMS, its automatic material system.
• E3D. Its V6 brass nozzles are listed with an input diameter of 1.75 mm, and the product is named for that size.
• LulzBot. Its TAZ Pro dual extruder tool head is sold as a 2.85 mm part, with "Filament Diameter 2.85mm" in its spec table.

Because the extruder, nozzle, and any multi-material unit are each specified for one diameter, buy the size your printer's maker lists. If you're unsure, don't load a spool to find out. Check the spec page first, as described below.

How do I find which filament diameter my printer uses?

The quickest answer is on the maker's own spec page, usually in a row labeled "Filament Diameter." These are examples from the makers' pages:

If your printer is in our printer directory, its page shows the filament diameter wherever the maker's documentation lists one, with links to the sources. Every printer in that directory with a recorded diameter is a 1.75 mm machine, including the Bambu Lab, Prusa, and Creality models.

If you can't find a spec page, Simplify3D notes that "many spools of plastic also include the correct diameter on the packaging," so the label on the spool that came with the printer is another place to look.

How much diameter varies: published tolerances

No spool is exactly 1.75 mm along its whole length. Filament makers publish a tolerance, the most the diameter is meant to stray from the nominal size. These figures come from the makers' own pages:

Prusa's under-extrusion article gives "the industry standard of variations in diameter" as "+/- 0.05 mm," and says some filaments vary in thickness "due to quality or infused materials like wood, which will cause unexpected changes in the volume of extruded filament." Prusament says it measures diameter "more than 4700× per second" during manufacturing and publishes averaged measurement data for each spool.

Checking a spool yourself

ELEGOO's wiki lists symptoms of filament with too much diameter variation or a non-round cross-section: inconsistent extrusion, uneven surfaces, extruder slipping or abnormal noise, filament that won't pass smoothly through the feed tube or extruder, and localized under-extrusion or bulging. Its check, in short:

1. Pull out about 1 meter of filament and mark 5 to 6 points, roughly every 15 to 20 cm.
2. Measure each point with a zeroed digital caliper, then rotate the filament 90° and measure again. A big difference between the two readings at one point suggests an oval cross-section.
3. If only a short section is out of tolerance, cut it out and keep watching the rest. If several sections vary significantly, ELEGOO says to stop using that roll.

ELEGOO adds that if the diameter "varies randomly at different positions, adjusting the filament diameter setting or flow ratio in the slicer cannot accurately compensate."

The slicer's filament diameter setting

Simplify3D explains that each slicer profile includes settings "used to determine how much plastic the 3D printer should extrude," and the filament diameter is the first one it tells you to check. The setting has to match what's loaded.

• UltiMaker Cura. Cura's base printer definition describes its Diameter setting as: "Adjusts the diameter of the filament used. Match this value with the diameter of the used filament." That base definition defaults to 2.85 mm, so if you build a custom printer profile for a 1.75 mm machine, check this value.
• Simplify3D. Its under-extrusion guide says "the first thing you want to verify is that the software knows the filament diameter that you are using," and that you'll find it under Edit Process Settings, on the Other tab. It suggests measuring with calipers "to make sure that you truly have the correct diameter specified in the software."

Check it especially when you create a custom printer or filament profile, or import one from elsewhere. If prints show gaps and thin walls, the diameter setting is one of the checks in our under-extrusion guide.

Every spool on this site is 1.75 mm

Every verified filament in our catalog, across PLA, PETG, ABS, TPU, and specialty filaments such as ASA, nylon, and polycarbonate, is a 1.75 mm spool, as listed by its maker. If your printer takes 2.85 mm filament, none of the spools we list will fit it, and you'll need to shop for that size elsewhere. If it takes 1.75 mm, any of them will match on diameter, though you should still check the maker's material and nozzle requirements.

Quick reference

Before you buy filament

• Find "Filament Diameter" on your printer maker's spec page, or check your printer's page in our printer directory.
• Treat a "3 mm" listing as 2.85 mm, and only buy it for a 2.85 mm printer.
• Look for a published diameter tolerance on the filament maker's page. The makers above publish figures from ±0.02 to ±0.04 mm.
• Confirm the filament diameter setting in your slicer matches the spool, especially in custom or imported profiles.
• If a new spool extrudes unevenly, measure it at several points before changing slicer settings.

Ready to choose? The PLA filament shortlist lists verified 1.75 mm PLA spools with each maker's published specifications. If you're still deciding on a material, start with the filament finder.