Filament Usage & Cost Calculator
What is left on a spool once you subtract the spool, and why a kilogram of ABS is 19 per cent more material than a kilogram of PLA.
What a kilogram buys, by material
Diameter tolerance is an area spec
You buy by weight and print by volume
Which means the denser material is worse value at the same price per kilogram, and nothing on the shelf says so. A kilogram of PLA at 1.24 g/cm³ is 806 cm³; a kilogram of ABS at 1.04 is 962. That's 19% more material for the same money — 48 parts against 40 for the same 20 cm³ object. At $25/kg it's $0.026 per cm³ against $0.031.
And the spool weight trap is worse than it looks. A "1 kg" spool is a kilogram of filament plus the spool — 130 g for cardboard, up to 330 for a heavy plastic core. Weigh a part-used spool at 600 g with a 225 g core and you have 375 g, not 600: the naive reading overstates by 60%. Worse, the error grows as the spool empties — by the time the scale reads the spool's own weight you believe you have that much filament and you have none. It's least reliable exactly when you most need it.
Diameter tolerance is an area spec wearing a length label. Cross-section goes as the square of the diameter, so the familiar ±0.05 mm on 1.75 is ±5.8% of the plastic delivered per millimetre — not the 2.9% the number suggests. That's the same error the extruder has to absorb as flow variation, which is why tolerance is worth paying for and why measuring your actual average diameter improves accuracy for nothing.
- Weigh the empty spool once and write it on the side. Manufacturers vary from 130 g to over 300, some print the tare and many don't. A figure you've measured beats every table including this one.
- 2.85 mm filament carries 2.65× the plastic per millimetre of 1.75 — so the same length is a very different amount of material, and extruder steps don't transfer between them.
- Nylon corrupts a weigh-back in a way nothing else does: it absorbs water from the air, so a spool genuinely weighs more after a fortnight than when you last used it. If the weigh-back says you gained filament, that's what happened — and it wants drying.
- A part quoted in grams means different things in different materials. A 20 cm³ part is 25 g in PLA and 21 in ABS, so comparing anyone else's gram figures without their material is comparing nothing.
How to use
- Weigh the whole spool and subtract the spool itself, not the reading.
- Compare materials on cost per cubic centimetre, not per kilogram.
- Enter your measured filament diameter rather than the nominal one.
- Weigh an empty spool once and write the figure on the side.
Frequently asked questions
How much filament is left on my spool?
Weigh the whole thing and subtract the spool. A "1 kg" spool is a kilogram of filament plus the spool, which runs about 130 g for cardboard and up to 330 for a heavy plastic core — so 600 g on the scale with a 225 g spool is 375 g of filament, not 600. Taking the reading at face value overstates it by 60 per cent.
Why does the spool weight matter so much?
Because the error grows as the spool empties, which is exactly when the number matters. At 600 g measured you are wrong by 60 per cent; by the time the scale reads the spool own weight you believe you have that much filament and you have none. A fixed subtraction becomes an ever-larger proportion of an ever-smaller remainder.
How many metres of filament are in a kilogram?
About 335 metres of 1.75 mm PLA, and 400 metres of ABS — because ABS is less dense. The calculation is weight divided by density to get volume, then volume divided by the filament cross-section of 2.405 mm2. Any figure quoted without the material is only right for one material.
Is ABS cheaper than PLA to print with?
Per unit of finished part, usually yes, and it is invisible on the shelf. You buy filament by weight and print by volume, so density decides how much part a kilogram makes: PLA at 1.24 g/cm3 gives 806 cm3 and ABS at 1.04 gives 962 — 19 per cent more for the same money. At the same price per kilogram that is 2.6 cents a cubic centimetre against 3.1.
What is the cost per cubic centimetre of filament?
Price per kilogram divided by the volume a kilogram contains, which is 1000 divided by the density. At $25 a kilogram that is $0.031 per cm3 for PLA, $0.032 for PETG and $0.026 for ABS. It is the only fair way to compare two materials, because a cubic centimetre is what a printed part is made of and a kilogram is not.
How much does a 3D printed part cost in material?
Volume times cost per cubic centimetre. A 20 cm3 part is about 62 cents in PLA at $25 a kilogram, and 52 in ABS at the same price. The same part weighs 25 g in PLA and 21 in ABS, which is why comparing anyone else gram figures without knowing their material compares nothing at all.
Does filament diameter tolerance matter?
More than the number suggests, because cross-section goes as the square of the diameter. The familiar plus or minus 0.05 mm on 1.75 mm filament is plus or minus 5.8 per cent of the plastic delivered per millimetre, not 2.9. That is the same variation the extruder has to absorb as flow error, which is why a tighter tolerance is worth paying for on dimensionally critical work.
Should I measure my filament diameter?
It is worth doing once per spool and entering the average. Callipers at a few points along the filament take a minute, and a real figure instead of the nominal one improves dimensional accuracy for nothing — most slicers have a filament diameter field precisely for this, and most people leave it at 1.75 forever.
How much more material is 2.85 mm filament than 1.75 mm?
Exactly 2.65 times per millimetre of filament, since area goes as the square of diameter. It means extruder calibration figures do not transfer between the two at all, and it means the same length of filament is a very different amount of plastic — which catches people converting a printer or reading advice written for the other size.
Why does my nylon spool weigh more than it did?
Because it has absorbed water from the air, which genuinely adds weight. Nylon is the worst for it but PETG and TPU do it too. It corrupts a weigh-back estimate in a way nothing else does — if the scale says you gained filament since last time, that is what happened, and the spool wants drying before it wants printing.
Do different colours of the same filament weigh differently?
Slightly, because pigment and any filler change the density. The effect is small compared with the difference between materials, but it is real for heavily filled filaments — glow-in-the-dark, metal-fill and wood-fill can be noticeably denser than the base polymer, so a kilogram of them makes a smaller part than a kilogram of plain PLA.
What is the best way to track filament use?
Weigh the spool before and after, having subtracted the tare once and written it on the spool. Slicer estimates are usually good but they do not include purge, priming, failed prints or the last few metres you could not use — and those are exactly the losses worth knowing about, because they are the ones you can reduce.
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