What this calculator works out
This calculator costs a print from the filament it uses, the spool price and the spool weight.
Filament is usually the smaller part of a print's cost. Electricity, failed prints and the printer's own depreciation frequently exceed it, and none of them appear here.
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Before you cost a print
- Filament used comes from the slicer, which reports it in grams and metres before you print.
- Spool weight means the filament, not the spool and filament together. A '1 kg spool' holds 1 kg of filament.
- The figure excludes electricity, wasted prints, support material and the printer's depreciation.
- Failed prints are a real cost. A 20% failure rate on a long print doubles the effective filament cost.
For a typical desktop printer drawing 100 to 150 watts, a ten hour print uses around 1 to 1.5 kWh — perhaps 25 to 40p. That is often comparable to the filament. Add an occasional failure and the printer's own cost spread over its life, and filament is frequently under half the true total.
How this calculator works
A proportion of the spool price:
Cost = filament used in grams × spool cost ÷ spool weight in gramsThe calculation is a simple proportion, so the units cancel provided the two weights match. Slicers report both grams and metres; grams is the figure to use, since filament is sold by weight.
Worked example: a 45 gram print
Using the default figures — 45 g of filament from a £22 spool holding 1,000 g:
- Filament cost: £0.99
Under a pound, which is why filament rarely feels like the constraint. If that print takes eight hours on a 120 W printer, the electricity is roughly 1 kWh — about 25p at typical rates. And if one print in five fails, the effective filament cost becomes £1.24. The honest total is closer to £1.50 than to 99p, and the gap grows with print time rather than with size.
Common mistakes
- Counting filament only. Electricity, failures and depreciation are all real.
- Using the gross spool weight. The stated weight is the filament alone.
- Ignoring support material. The slicer includes it, so use the slicer's figure.
- Forgetting failed prints. They consume filament and time and produce nothing.
- Pricing a service by filament cost. It substantially undercharges the time involved.
Frequently asked questions
What does a 3D print cost to run?
Filament, electricity and a share of the printer's cost over its life. A desktop FDM printer drawing 100 to 150 watts uses roughly 1 kWh per eight to ten hours, so electricity is usually a similar order to filament for a typical print. Resin printing has different economics, with more expensive material and additional consumables for washing and curing.
How do I reduce filament use?
Lower infill where strength allows — 15 to 20% is plenty for most decorative and light functional parts. Orient the model to minimise supports, which are pure waste. Hollow large solid volumes. Between them these commonly halve the material on a print that was sliced without thought.
Does filament type change the cost?
Substantially. Basic PLA is the cheapest; PETG and ABS cost somewhat more; specialist filaments with carbon fibre, wood fill or engineering polymers can cost several times as much. Density also differs, so the same volume of part weighs different amounts in different materials.
How should filament be stored?
Dry and sealed. PLA, and PETG and nylon far more so, absorb moisture from the air, which causes stringing, poor layer adhesion and audible popping while printing. Sealed boxes with desiccant are the usual approach, and a filament dryer will recover a spool that has already absorbed moisture.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
Related tools
References
- Health and Safety Executive — ventilation and emissions from 3D printing, and safe use of electrical equipment
- GOV.UK — product safety and electrical equipment standards
Sources are checked at publication and can change — how I choose and check references.