How filament cost per gram really works
Why spools are priced per kilogram, how to turn that into a per-gram and per-print cost, and the hidden extras that a material-only figure leaves out.
Per kilogram is the anchor price
Almost every filament spool is sold by weight, and the standard spool holds one kilogram of plastic. That is why the calculator asks for a price per kilogram rather than a price per spool. If your spool holds a different amount, divide what you paid by the kilograms it contains to get a fair per-kilogram figure. From there, one gram of filament costs the spool price divided by 1000, so a 25 dollar spool works out to 2.5 cents per gram.
From grams to a single print
The slicer does the hard part by estimating how many grams a model will use once it is sliced with your chosen layer height, infill and supports. Multiply that weight by the per-gram cost and you have the material cost of the print. A 250 gram print on a 30 dollar spool is a quarter of the spool, or 7.50 dollars. Changing infill from 15 to 40 percent can noticeably raise the grams, so reslice if you tweak settings before trusting an old number.
What a material-only cost leaves out
Filament is usually the largest single input, but it is rarely the whole story. Electricity to run the printer, gradual wear on the nozzle and motion system, the occasional failed print, post-processing supplies and your own time all add up. For a hobby print none of this may matter, but if you sell prints you should layer these costs on top and add a margin. Treat the filament figure here as the solid foundation you build a real quote around.
Cutting the cost per print
The cheapest gram is the one you never print. Lowering infill where strength allows, reducing wall count, and orienting parts to need fewer supports all trim grams directly. Buying filament in multi-spool packs lowers the per-kilogram price that feeds this calculator, and printing several small parts on one plate spreads fixed waste like purge lines across more useful output. Small habits compound quickly across a busy print farm.