How to Calculate Filament Cost Per Gram

Filament cost per gram is the building block for every other cost calculation you'll do. It's one division.

The formula

cost per gram = spool price ÷ spool weight in grams

A $22 spool that weighs 1000g (1kg) works out to 2.2 cents per gram. A $22 spool that weighs 750g works out to about 2.9 cents per gram, the smaller spool is more expensive per gram even though the sticker price is identical.

Watch for net vs. gross weight

The "1kg" on a spool label almost always means 1000g of filament by itself, the empty spool adds extra weight on top of that, which is why a full spool weighs more than a kilogram on a kitchen scale. The real exception to watch for is a handful of brands that sell noticeably less than 1000g of actual filament under "1kg" pricing and positioning, Prusament ships 970g, Fiberlogy's standard spool is 850g, and some PETG lines run as low as 750g. Slicer software usually reports how much filament (by weight) a given model will use, and most printers or filament runout sensors can give you a real remaining-weight reading. When in doubt, weigh a full spool yourself on a kitchen scale before you print anything, it takes thirty seconds and removes the guesswork.

From cost per gram to cost per print

material cost = filament used in grams × cost per gram

Slice your model, note the estimated filament weight, and multiply. That's your material cost, before electricity, machine wear, or labor get added in.

Why this matters more than the sticker price

Comparing spools by their listed price alone is misleading once spool weights differ, or once specialty finishes (silk, matte, glow-in-the-dark) come with a premium. Cost per gram is the only fair way to compare two different filaments, or the same filament from two different brands.