Filament calculator
Three questions about filament, answered in one place: how many metres are in so many grams, how much is left on the spool you are holding, and whether that is enough for the print you are about to start.
Everything is worked out on this page as you type. Nothing is sent anywhere and nothing is saved.
Length and weight
Filament is sold by weight and used by length, so the two have to be converted all the time. The conversion depends on only two things: how thick the filament is, and how dense the plastic is.
A kilogram of 1.75 mm PLA is about 335 metres. The same kilogram of 2.85 mm PLA is only about 126 metres, because each metre holds more than two and a half times as much plastic. Density matters too: ABS is lighter than PLA, so a kilogram of 1.75 mm ABS is closer to 400 metres, while PETG is slightly heavier and comes in a little under PLA.
The densities in the list are the typical figures manufacturers publish. A particular brand can be a few per cent either way, and filled filaments — wood, carbon fibre, glow-in-the-dark — can differ more. If the spool’s label gives a density, type it in.
How much is left on the spool
Weighing is the reliable way. Put the spool on a kitchen scale and take off the weight of the empty spool. The empty spool is the hard part: it varies a lot between brands, from around 130 grams for a cardboard spool to 250 grams or more for a heavy plastic one. The best figure is one you have weighed yourself — keep an empty spool of each brand you buy and weigh it once.
With no scale, measure the filament instead: the diameter across the outside of the wound filament, the diameter of the hub it is wound on, and the width inside the spool. The filament fills about four fifths of that ring, and the rest is gaps between the strands. It is a rough answer, good to perhaps fifteen per cent, and it is enough to tell a nearly full spool from a nearly empty one.
Is it enough for the next print?
Your slicer shows the grams a print needs before you start it. Compare that with what is left, and leave a margin: the purge line, a failed first layer that has to be restarted, and the last metre or so that never makes it off the spool all use filament the slicer did not count.
The calculator adds ten per cent for that. If what is left is close to the line, most printers can pause for a filament change partway through — M600 on Marlin and Prusa printers — and a filament runout sensor will stop the print rather than let it run dry.
Checking the diameter
Measure the filament with calipers in a few places along a metre of it. Good filament stays within two hundredths of a millimetre of its stated size. That small difference changes the length in a kilogram by about two per cent, which is why a slicer’s filament estimate and the length you actually get can disagree slightly.
The next question
Questions
- How many metres are in a 1 kg spool?
- About 335 metres of 1.75 mm PLA, about 327 metres of PETG, and close to 400 metres of ABS. At 2.85 mm, a kilogram of PLA is about 126 metres.
- How much does an empty spool weigh?
- Anything from about 130 grams for cardboard to 250 grams or more for plastic, depending on the brand. Weigh an empty spool of the same brand once and use that figure every time.
- Why does my slicer give a different length?
- Slicers use the diameter and density set in their filament profile. If those differ from the values here, so will the result. Set both the same and the numbers agree.
- Can I work out the filament a model needs?
- Yes, in the 3D printing cost calculator. Drop the model or its G-code in and the grams and metres are worked out for you.