The arithmetic is not complicated:
Cost = grams used × (spool price ÷ 1000)
A 1 kg spool at $22 costs 2.2 cents per gram. A 40-gram print costs 88 cents of plastic. Your slicer tells you the grams before you press go.
What is worth understanding is which of the other costs matter, because the intuitive ranking is wrong.
Electricity is close to noise
A typical desktop printer draws somewhere around 100–150 W averaged over a print — the hot end and bed cycle rather than running continuously, so peak draw is misleading.
At 120 W and the US average residential rate of roughly 16 cents per kWh, a ten-hour print uses about 1.2 kWh, which is about 19 cents.
That ten-hour print probably used 100 g of filament, or $2.20. Electricity is under a tenth of the material cost, and it will stay there unless your rate is extraordinary. People who carefully account for power while ignoring failed prints have optimized the wrong term.
The failure rate is the real cost
A 5% failure rate raises your effective material cost by about 5%. That sounds mild until you notice failures are not distributed evenly: prints fail more often near the end, when the most filament has already been laid down and the most hours have been spent.
A 20-hour print that fails at hour 18 costs nearly the full material and all of the time. This is why a $30 spool of filament that prints reliably is cheaper than a $18 spool that fails one print in ten — and it is the only place in this arithmetic where spending more money reliably saves money.
Weighing what is left on a spool
Slicers estimate grams for a print. For the spool itself, weigh it and subtract the empty spool.
Empty spool weights, approximately:
- Plastic spool: 200–250 g
- Cardboard spool: 130–180 g
Manufacturers rarely print this on the packaging, so weigh one empty spool of each brand you buy and write it on the side. After that, remaining filament is a subtraction.
For reference, 1 kg of 1.75 mm filament is roughly 330 m of PLA and 320 m of PETG — the difference comes from density, 1.24 against 1.27 g/cm³.
Where the grams actually go
Two settings dominate the number your slicer reports, and neither is the one people reach for first.
Infill percentage is the obvious lever, and it is less powerful than it looks. Above about 40%, extra infill adds substantial weight for very little strength — the returns flatten hard. Below about 15%, the top surface starts needing more layers to bridge the gaps, which claws back some of what you saved.
Wall count is the lever that matters. For most functional parts, strength comes from the perimeters, not the infill. Two walls at 25% infill will usually be weaker and heavier than four walls at 10%. If you are trying to reduce cost without losing strength, add walls and cut infill rather than the reverse.
Supports are pure waste by definition — every gram becomes rubbish. Reorienting a part to avoid them often saves more filament than any infill change.
What a spool is worth per print
A rough table for a $22 kg spool, using typical print weights:
| Filament | Cost | |
|---|---|---|
| Phone stand | 40 g | $0.88 |
| Small functional bracket | 15 g | $0.33 |
| Benchy | 12 g | $0.26 |
| Storage box, 150 mm | 180 g | $3.96 |
| Large cosplay piece | 600 g | $13.20 |
The practical conclusion for most people is that filament is not where the money goes. Time is, and failed prints are.
FAQ
How much does a 3D print cost?
Grams used multiplied by spool price divided by 1000. A 1 kg spool at $22 works out to 2.2 cents per gram, so a typical 40-gram print costs under a dollar in material.
How much electricity does a 3D printer use?
Roughly 100–150 W on average during a print. At US average rates that is about 2 cents an hour, which is under a tenth of what the filament costs.
How much filament is left on my spool?
Weigh the spool and subtract the empty spool weight — about 200–250 g for plastic, 130–180 g for cardboard. Weigh one empty spool per brand and write the number on it.
How long is 1 kg of filament?
About 330 m for 1.75 mm PLA and about 320 m for PETG. The difference is density.
Does higher infill make a part much stronger?
Not past about 40%. For functional parts, adding perimeters is more effective per gram than adding infill, and often lighter as well.