Basics
In 3D printing, time costs more than plastic
The cost of a print breaks down into five parts: filament or resin; machine time (depreciation plus wear parts such as nozzles, belts and FEP film); electricity; post-processing labour — support removal, washing, curing, sanding; and a margin for failed prints. Hobbyists tend to count only the plastic, but for a palm-sized part the material is usually well under a dollar, and machine time plus finishing dominate. That's why print-service quotes run several times the material cost.
An FDM part isn't solid. Its skin is a few nozzle-widths of perimeter walls plus solid top and bottom layers, and the inside is filled to a set percentage with a grid, gyroid or similar infill. Filament use is therefore not 'volume × infill' but 'shell volume + interior volume × infill'. Shell volume is roughly surface area × wall thickness, and the smaller the part, the more of it is shell — which is why dropping infill on small parts barely changes their weight. Drop in an STL and the calculator uses the measured surface area; without a file it estimates area from a shape factor.
Shell volume: V_shell = min(V, A × t_wall) Part volume: V_part = V_shell + (V − V_shell) × infill Filament mass: m = V_part × (1 + support) × (1 + waste) × ρ Print time: t ≈ V_part × (1 + support) ÷ Q_avg + setup time SLA resin: ml = V × (1 + support) × (1 + waste), time = (height ÷ layer height) × seconds per layer Cost: material + hours × machine rate + kW × hours × electricity price + labour + failure margin
| Material | Density (g/cm³) | Length per kg (1.75 mm) | Notes |
|---|---|---|---|
| PLA | 1.24 | ≈ 335 m (1,100 ft) | Easy and accurate; softens near 60 °C (140 °F) |
| PETG | 1.27 | ≈ 327 m (1,074 ft) | Tough, water-resistant; prone to stringing |
| ABS | 1.04 | ≈ 400 m (1,312 ft) | ~95 °C heat resistance; warps and smells — needs an enclosure |
| ASA | 1.07 | ≈ 389 m (1,275 ft) | ABS-class heat plus UV resistance for outdoor parts |
| TPU 95A | 1.21 | ≈ 344 m (1,128 ft) | Rubber-like and flexible; print slowly |
| PC | 1.20 | ≈ 347 m (1,137 ft) | Top-tier strength and heat; needs a hot nozzle |
| Standard SLA resin | ≈ 1.1 g/ml | — | Best surface and detail; post-cure required |
Example — a 50 cm³ enclosure in PLA on a fast printer
Estimating surface area with the 'typical' shape factor gives about 122 cm². With 1.2 mm walls the shell is 14.7 cm³; 20 % infill of the remaining 35.3 cm³ adds 7.1 cm³, for 21.7 cm³ of part. Adding 10 % support and 5 % waste gives 25.1 cm³, or about 31 g of PLA — 43 % of the solid weight (≈ 72 g) despite '20 % infill'. At an average 15 mm³/s it prints in about 27 minutes plus 10 minutes of setup. Using the default rates, cost is $0.62 material + $0.61 machine time + $0.01 electricity, plus a 10 % failure margin: about $1.37. Material is less than half.
Example — a 20 cm³ figurine in resin, 60 mm tall
At 0.05 mm layers that's 1,200 layers; at 8 s per layer, 2 h 40 min plus 10 minutes of setup. Resin comes to 24 ml with 15 % supports and 5 % waste (about $1.09), but machine time ($2.83) and consumables like IPA and gloves ($1.50) cost more. Because an MSLA printer exposes a whole layer at once, ten figurines on the same plate take almost the same time as one — so per-part cost falls sharply when you batch.
Pitfalls
Common mistakes
- Reading infill percentage as weight percentage: 20 % infill applies only to the interior. With walls included, parts typically weigh 30–60 % of solid — more so for small parts.
- Wrong STL units: an STL exported in inches but read as millimetres comes out 1/16,387 of its true volume; one exported in metres, a billionth. Sanity-check the X×Y×Z size first.
- Estimating time from advertised speed: '500 mm/s' is peak travel. Perimeter slow-downs, acceleration limits and minimum layer time pull the average flow far lower — confirm time in your slicer.
- Assuming zero failures: first prints of a new geometry, tall parts and fussy materials like TPU or ABS often need a reprint. Budget 10–20 %.
- Leaving out SLA consumables: on top of resin there's IPA, nitrile gloves, FEP film and vat wear, and curing time.
- Measuring a non-manifold mesh: an STL with holes gives a nonsense volume. Check and repair the mesh in your slicer first.
In practice
Tips from KEMI's print room
The most reliable way to cut cost is orientation: fewer supports means less material, less time and less clean-up all at once. Strength depends more on wall count than on infill, so functional parts are efficient at 20–30 % infill with 3–4 walls. Thicken walls around screw bosses or use heat-set inserts, and choose PETG or ASA over PLA for outdoor or warm environments. If you're making an enclosure for a PCB, design it straight from the board-outline and connector DXF to avoid fit problems. And if the size, material or quantity is beyond your own printer, send the STL to KEMI for a 3D printing quote.