$30.46, for a spool bought at $22/kg and consumed on a machine drawing 100 W at the US average electricity rate, with a 5% failure allowance and 30 cents an hour set aside for machine wear.
The retail price of the spool is $22.00 of that. Everything else is what the printer costs you while it turns the spool into parts.
| Term | Amount | Where it comes from |
|---|---|---|
| Filament | $22.00 | 1 kg at $22/kg |
| Electricity | $0.38 | 2.184 kWh at 17.5 cents |
| Machine time | $6.55 | 21.8 hours at 30 cents |
| Failure allowance | $1.52 | 5% of attempts scrapped |
| Total | $30.46 |
Where the 21.8 hours comes from
A kilogram of PLA at 1.24 g/cm³ is 806 cm³ of plastic — 335 m of 1.75 mm filament. Extruding all of it at 0.2 mm layers and 150 mm/s through a 0.4 mm nozzle demands 13.5 mm³/s of flow, which puts 21.8 hours of machine running time behind a single spool.
That figure is the reason machine time outweighs electricity by seventeen to one here. Nozzles, belts, plates and hotends wear by the hour whether or not you account for them; the power meter barely moves.
The two terms people get wrong
Electricity is smaller than almost everyone guesses. 2.184 kWh across a whole spool costs 38 cents in the United States, and even at the German average rate — the highest in this site's rate table — it comes to €0.84.
Machine time is bigger than almost everyone guesses. 30 cents an hour is a deliberately modest allowance: a machine expected to last a few thousand printing hours before its belts, hotend and build plate need replacing is already worth several cents an hour before any consumable is counted. Set that term to zero and the spool appears to cost $23.56, which is roughly the number most published per-spool figures give — and the one nobody can reconcile with their own parts bill at the end of the year.
What changes it most
Spool price, by a wide margin. PLA runs from $15 to $28 a kilogram at mainstream retail, so the filament term alone swings by thirteen dollars — more than twice the entire machine-time term and over thirty times the electricity.
After that, printing speed. Everything in the machine-time and electricity columns is proportional to hours, so the same kilogram pushed through a 0.6 mm nozzle at higher flow costs materially less to convert even though the plastic price does not move.
Put your own spool price, wattage and hourly machine allowance into the print cost calculator, or read how the electricity term is derived in the electricity cost method.