Start with grams, not spool price
Material cost per print = grams used × price per gram. Price per gram = the price you paid ÷ the net filament weight in grams. For a 1 kg spool, divide its price by 1,000. Use your own supplier price and include support, brim and purge material in the grams estimate.
Density changes the weight
PLA is approximately 1.24 g/cm³ and PETG approximately 1.27 g/cm³. For the same deposited volume, PETG therefore weighs slightly more. Actual density depends on the formulation, including fillers and additives; use the manufacturer’s figure when available.
Volume × density gives weight. A geometry estimate also needs to account for walls and infill: a mostly hollow print does not contain the full solid model volume in plastic. Check the resulting grams against your slicer.
Temperature and speed affect the whole job
PETG generally uses higher nozzle and bed temperatures than PLA, but follow your filament and printer guidance. Power use depends on the machine, temperature settings, ambient conditions and print duration; a hotter setpoint alone does not tell you the total energy.
Suitable print speeds and volumetric flow limits differ by filament, hotend and quality target. PETG may need different speeds, cooling and retraction from PLA. Do not assume a fixed speed penalty: compare your tested slicer profiles and their time estimates.
Compare complete costs
- Use the same part requirements and a suitable profile for each material.
- Compare estimated grams multiplied by your own price per gram.
- Add electricity, machine wear, expected reprints and hands-on finishing time.
- Choose a material that suits the part’s use, not only its quoted cost.
PrintQuote’s material library lets you keep density and your price per kg separate. Estimates are a starting point; check against your slicer and actual prints.