How to Calculate Filament Cost per Print
5 min readUpdated
Filament is the easiest cost to see and still easy to get wrong. The slicer gives you grams, the spool gives you a price, and the gap between the two is where supports, purge and leftovers hide.
Price per gram
Use the net weight printed on the label — 1 kg spools contain 1,000 g of filament; the empty spool is extra. Some brands sell 750 g, 800 g or 2–3 kg spools, so always check.
A $25 spool of 1 kg is $0.025 per gram.
Getting the grams right
Slice the model with your real settings and read the total weight. Make sure it includes:
- Supports, brim and raft.
- Prime tower and purged filament for multi-colour prints. For small multi-colour parts, the purge can be as heavy as the part itself.
- Every filament used — price each one at its own spool price.
Example: a 96 g model + 9 g of supports and brim + 15 g of purge = 120 g. At $0.025 per gram that is $3.00, not the $2.40 the model alone suggests.
Estimating weight from volume
Without a slicer you can estimate from the model volume: weight = volume (cm³) × density (g/cm³). Typical densities:
| Material | Density (g/cm³) | 50 cm³ solid weighs |
|---|---|---|
| PLA | 1.24 | 62 g |
| PETG | 1.27 | 64 g |
| ABS | 1.04 | 52 g |
| ASA | 1.07 | 54 g |
| TPU | 1.21 | 61 g |
Real prints are not solid. With 15% infill, a part is a shell plus sparse inside, so it weighs far less than its solid volume suggests — how much less depends on its shape. Slice&Price's STL preview estimates weight from the volume and the infill you choose.
Comparing materials
Density changes the cost per part. At the same price per kilo, the same model in ABS uses about 16% less filament by weight than in PLA, and PETG about 2% more. A cheaper spool is not always the cheaper part.
Waste you should count
- The last few metres of a spool that are too short to finish a print.
- Failed prints — covered by the failure rate in the full pricing formula.
- Test prints and calibration when you start with a new material.
To reduce purge in multi-colour prints, group colours on fewer layers, flush into infill or a sacrificial object, and keep the prime tower as small as your slicer allows.
Frequently asked questions
How do I calculate filament cost per print?
Multiply the grams reported by your slicer (including supports and purge) by your price per gram, which is the spool price divided by the net filament weight.
Does a 1 kg spool include the spool itself?
No. The 1 kg is the filament; the empty spool weighs extra, often around 150–250 g. Weigh one empty spool of each brand so you can check how much filament is left.
Which filament is cheapest per part?
Compare cost per part, not per kilo. Lower-density materials such as ABS use fewer grams for the same volume.