Filament Weight to Length

Slicers talk in both grams and meters, spools are sold by weight, and the leftover on a part-used reel is anyone's guess. This converts between the two for any filament: how many meters are in a weight, or what a length weighs, using the diameter and the material's density, so you can see what is left, buy enough, or price a print by either.

Filament is a rod, so it is just geometry

A reel of filament is one long round rod, and its weight is its volume times the plastic's density. The volume is the cross-section area, set by the diameter, times the length. So a weight converts to a length and back once you know the diameter and the material. The diameter matters a lot because area goes with its square: 2.85 mm filament is far heavier per meter than 1.75 mm, so the same kilo is many fewer meters.

Density changes the meters per kilo

Different plastics weigh different amounts for the same size, and that changes how far a kilogram goes. PLA is fairly dense, so a kilo is around 330 meters of 1.75 mm; lighter ABS gives a bit more length per kilo, denser PETG a bit less. If you swap materials but keep buying by the kilo, the length you get shifts, which matters when a print is quoted in meters. Pick the material here and the density is handled for you.

How much is left on the spool

The most useful trick is weighing a part-used spool. Weigh it, subtract the empty reel's weight, which is printed on many spools or can be weighed once, and you have the filament weight remaining. Put that into length mode and you know whether there is enough to start a print without running out partway. No guessing by how fat the reel looks, which is unreliable because the core and the winding fool the eye.

Grams, meters, and buying right

Slicers show a print's filament as both a length and a weight, and this lets you move between them for whatever you need: convert a meter figure to grams to see how many spools a big job needs, or to price the plastic by weight. It also gives grams per meter, a handy constant for your filament, so you can estimate a print's cost from its length in your head once you know that number.

More MakerKiln tools

• filamentFilament CalculatorFilament a print uses and what it costs, from the model and your spool price.→
• print cost3D Print Cost CalculatorFilament, power and wear cost of a print, with a price to charge.→
• flow rateVolumetric Flow Rate CalculatorThe flow a print asks of your hotend, or the top speed it allows.→

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