Convert geometric volume into material mass
When a slicer provides filament grams, use that because it already reflects shells/infill and often supports. If only a trustworthy closed STL volume is available, volume × density provides a solid-mass estimate before your explicit waste allowance.
Allocate the real spool cost
Material cost is the estimated grams divided by usable spool mass, multiplied by the actual price paid. This is more transparent than assuming one universal filament price.
Estimate electricity separately
Approximate kWh from average printer watts divided by 1000, multiplied by print hours. Real power varies during heating and motion, so use a measured average when available.
Direct cost is not a quote
A quote can include hands-on labor, machine wear, packaging, expected reprint risk, and platform/payment fees. Keep tax, shipping, discounts, design/licensing work, and any unentered overhead visible rather than hiding them in a mystery multiplier.
Model expected reprints without pretending every job fails
A failure allowance can be treated as an expected-cost adjustment: dividing the job cost by one minus the estimated failure rate. This is more transparent than quietly inflating filament cost, but the percentage should come from your own printer/job history when possible.
Gross margin is different from markup
A 30% margin means profit is 30% of the selling price, not 30% of cost. When fees are a percentage of selling price too, solve price from the remaining percentage after fee rate and target margin rather than applying a simple cost multiplier.