Ask ten people what a 3D print costs and most will quote the filament: "about 50 grams of PLA, so a dollar." That number is real, but it is only the first line of the bill. A useful estimate — whether you print for yourself, run a small Etsy shop or quote jobs for a print farm — has five parts.
The formula
cost = (material + electricity + machine wear + labor) × (1 + failure rate)
If you sell prints, the price is that cost plus a markup: price = cost × (1 + markup). Every part of the formula can be estimated from the STL file and a handful of numbers about your printer, which is exactly what our 3D print cost calculator does.
1. Material
material = grams × price per kg ÷ 1,000
The tricky part is the grams. A model's volume is not its weight, because almost nothing is printed solid. Slicers build a solid outer skin (the walls, plus top and bottom layers) and fill the inside with a sparse pattern such as 15% gyroid or grid infill. A good estimate therefore treats the shell and the infill separately:
- Shell volume ≈ surface area × wall thickness (typically 1.2 mm: three 0.4 mm lines)
- Infill volume = (solid volume − shell volume) × infill percentage
- Grams = (shell + infill) in cm³ × material density (1.24 g/cm³ for PLA)
Add a few percent for supports, brims and purge lines. Our guide to how much filament a print uses explains why the shell matters so much for small and thin parts.
For a quick sense of scale, 3D printing cost per gram tabulates material cost at common spool prices and works through four complete examples.
2. Electricity
electricity = hours × average watts ÷ 1,000 × price per kWh
Use the average power while printing, not the power supply rating. Most desktop FDM printers average 80–250 W; resin printers 40–80 W. At $0.18 per kWh, a 120 W printer costs about 2 cents an hour. Electricity is almost always the smallest line — see how much electricity a 3D printer uses for measured ranges by printer type.
3. Machine wear
machine = hours × hourly rate
Your printer loses value with every hour it runs, and it eats nozzles, belts, PTFE tubes, build plates, fans and — on resin printers — FEP film and LCD screens. Spread those costs over the hours you expect the machine to print:
hourly rate = (printer price + expected spare parts) ÷ lifetime printing hours
A $400 printer that runs 3,000 hours and needs $200 of parts over its life works out to $0.20 per hour. Hobbyists often ignore this line; anyone selling prints should not, because on long prints it can exceed the cost of the plastic.
4. Labor
labor = minutes ÷ 60 × hourly rate
Printing is mostly unattended, but slicing, starting the job, removing the part, cleaning supports, sanding and packing are not. Five to fifteen minutes per order is normal for simple parts; painted or assembled pieces take far longer. If you print only for yourself, leave labor at zero.
5. Failed prints
Spaghetti, warped corners and layer shifts happen. Rather than pretending they don't, add a failure buffer of 5–10% for PLA on a well-tuned printer and 15–25% for ABS, nylon, very large or very tall prints. The buffer is applied to everything above, because a failed print wastes time and electricity as well as filament.
A worked example
Take the sample model in the calculator: a twisted, six-lobed planter, 70 mm tall with 3 mm walls. Its volume is 48.3 cm³ and its surface area 326 cm². Printed in PLA on a fast bed slinger such as a Bambu Lab A1 or Prusa MK4S with 15% infill, 1.2 mm walls and 5% waste:
| Line | How | Cost |
|---|---|---|
| Material | 52.7 g × $20/kg | $1.05 |
| Electricity | 1.28 h × 100 W = 0.13 kWh × $0.18 | $0.02 |
| Machine wear | 1.28 h × $0.20/h | $0.26 |
| Labor | 0 min (personal print) | $0.00 |
| Failure buffer | 10% of the above | $0.13 |
| Total | $1.47 |
Notice that almost all of this part is shell: its walls are thin, so changing the infill from 15% to 50% adds only about 4 grams. On a chunky part such as a 50 mm solid sphere the opposite is true, and infill becomes the main lever on cost.
The same planter costs a little more on an older, slower bed slinger, because it spends almost twice as long on the machine. In resin it costs about twice as much as on the A1-class printer: printed solid, it uses more material, and resin is pricier per kilogram.
Where estimates go wrong
- Wrong units. STL files have no units. A model exported in metres or inches will look tiny or huge; check the dimensions first.
- Open meshes. If the mesh has holes, its volume is meaningless. The calculator reports open and non-manifold edges so you know when to repair the file.
- Supports and multicolor purge. Neither is part of the model. Tree supports might add 5–15%; an AMS or MMU color change can waste more plastic than the part itself on small multicolor prints.
- Print time. Average-speed estimates are rough. Once you have sliced a model, type in the slicer's time — it fixes the electricity and machine lines.
Checklist
- Load the STL and confirm the size and that the mesh is watertight.
- Pick the material and check the price per kilogram you actually paid.
- Set walls, infill and a waste allowance for supports.
- Choose your printer class, or type in your own wattage and machine rate.
- Add labor and a failure buffer, then a markup if you are selling — our guide to pricing 3D prints covers that step.