The short answer
About 95% of consumer printers — Ender, Bambu Lab, Prusa MK series, Anycubic — take 1.75 mm. The 2.85 mm standard (sold as 3 mm) lives almost entirely on Ultimakers and a few LulzBot and legacy machines.
Check in 30 seconds
- Read your current spool label — the diameter is printed on it
- Check the extruder and hotend specs in your printer manual
- Look at your slicer profile: it has a fixed filament-diameter field
- Still unsure? Check the manufacturer's page for your printer's diameter.
Can you convert?
No. Hotend, extruder gears, PTFE tube and nozzle are all diameter-specific hardware. Loading 2.85mm into a 1.75mm machine jams solid; 1.75mm in a 2.85mm machine under-extrudes into spaghetti.
TerraEco rolls
Every TerraEco roll is 1.75mm ±0.02mm, vacuum-sealed with desiccant. If your printer takes 1.75mm — and it almost certainly does — pick your material: beginner's guide.