The filament formula
Divide the spool purchase price by the usable grams on the spool. Multiply that cost per gram by total grams consumed by the job. For a $22.00, 1,000-gram spool, the baseline is $0.022 per gram. A job consuming 180 grams has $3.96 of filament cost.
($22.00 ÷ 1,000 g) × 180 g = $3.96Use the actual net filament weight stated for the product rather than the shipping weight. If a partly used spool has known damage or unusable material, base the calculation on the amount you reasonably expect to consume.
Use consumed material, not final-part weight
The customer receives the finished model, but the job may also consume supports, brims, skirts, purge towers, flushing waste, priming lines, and calibration material. The slicer’s total filament figure is normally a better pricing input than weighing only the completed part.
For a batch, use total material across the plate and set the correct sellable quantity. This spreads shared waste across the completed units. If the batch yields four parts and consumes 420 grams from a $24.99 kilogram spool, the material baseline is about $10.50 for the batch, or about $2.62 per finished part before failures.
Handling multiple filament prices
When colors or materials cost different amounts, calculate each one separately: grams of material A multiplied by its cost per gram, plus grams of material B multiplied by its cost per gram. The sum is the accurate material cost. If the calculator uses one spool field, translate that total into a weighted equivalent spool price or enter the difference in other batch costs.
100 g at $0.020/g plus 50 g at $0.030/g costs $3.50 total. For 150 g total consumption, the weighted rate is about $0.0233/g, equivalent to a $23.33 kilogram spool.
Account for failure without double-counting
You can model known purge and support material directly because the slicer predicts it. Random failed attempts are different: apply a failure reserve to the whole production cost, since a retry can also consume printer time, power, maintenance, and labor. Simply adding extra filament misses most of the risk.
Why material-only pricing breaks down
A small detailed object may use little plastic while occupying a printer for many hours. A customized object may require more communication and setup than printing. Packaging can cost as much as the filament. Selling fees are based on revenue, not grams. Material cost is a necessary fact, but it is not a selling price.
Use cost per gram to verify one line of the estimate. Then add machine, human, risk, and selling layers before choosing a margin. That produces a price you can explain and update when spool prices change.