Ask what a print costs and almost everyone answers in grams. The slicer prints a mass on the screen, filament has a price per kilogram, and the multiplication is easy. Electricity has none of those conveniences: the printer does not report it, the number changes with the material and the bed size, and the price per unit differs by a factor of four depending on where you live.
So it gets skipped. And when it does not get skipped, it usually gets computed wrong in a way that is worse than skipping it.
The two opposite errors
The first error is leaving it out. On a short print in PLA that is nearly harmless: a two-hour job on a mid-sized machine uses something like 0.2 kWh, which at most residential rates is a few cents against maybe eighty cents of filament. Rounding it to zero costs you almost nothing.
The second error is quoting the printer's power-supply rating as its consumption, and this one is genuinely destructive. Supply ratings in the region of 350 W to 1,300 W are published for machines that actually meter around 65 W to 130 W while printing. Treating the rating as consumption inflates the electricity term by five to ten times, and the resulting figure — several dollars for an overnight print — is alarming enough to change what people decide to make.
Both errors circulate widely. They point in opposite directions, which means the average of the published wisdom is roughly right and no individual figure can be trusted.
What the real numbers look like
A power-supply rating is a ceiling. Real consumption is whatever the bed, the hotend and the motors happen to be asking for at that instant, and once everything is up to temperature that demand falls a very long way short of the ceiling.
Reported plug-meter figures for popular machines cluster in recognisable bands. A small 180 mm open-frame printer sits near 55 to 65 W. A 250 mm class machine sits near 90 to 110 W. An enclosed 256 mm CoreXY sits near 110 to 120 W. A 350 mm or larger open bed runs 200 W and upward, and a machine with an actively heated chamber adds a continuous load on top of all of that.
Heat-up is genuinely large and genuinely brief. Several hundred watts for a minute or two, up to around 850 W on some enclosed machines for the first half-minute. Spread across a twelve-hour job and priced at the United States average, that spike is worth roughly a quarter of a cent. Shrink the job to a quarter of an hour and that same spike stops being a rounding error. The distinction matters only when the print is short.
Bed area is the whole story
Line up printer profiles by steady-state consumption and the ordering is almost entirely explained by one variable: how much heated bed is being held at temperature.
That makes sense physically. The hotend is a small thermal mass with a small surface area, insulated by a silicone sock, and it needs perhaps twenty to fifty watts to hold temperature once hot. The bed is a large flat plate, often uninsulated underneath, radiating and convecting into the room for the entire print. A 420 mm bed has more than five times the area of a 180 mm one, and it loses heat in proportion.
Two useful consequences follow. First, bed temperature is the highest-energy setting in your whole profile, so dropping it from 100 °C to 60 °C where the material allows is the single largest saving available. Second, a passive enclosure reduces energy use rather than increasing it. There is no heater in a passive enclosure; all it does is retain warmth the bed was radiating into the room at your expense. Only an actively heated chamber adds load.
When the term genuinely matters
Three situations.
Long prints on large machines. Twenty hours at 250 W is 5 kWh. In Germany that is over two dollars. Against maybe six dollars of filament, that is no longer noise.
High-temperature materials. A 110 °C bed and a heated chamber consume substantially more than a 60 °C bed and no chamber, for the same print time.
Anyone running more than one machine commercially. Four printers averaging 150 W each, running twelve hours a day, is 7.2 kWh a day and over 2,600 kWh a year. At a European rate that is a four-figure annual bill, and it belongs in the pricing.
For a single hobby printer running PLA, electricity is real but small, and the honest thing to say is that filament and failed prints will dominate your costs long before the meter does.
The half-day that fixes this permanently
The instrument that ends the argument is a plug-in energy meter, and it is a smaller purchase than a spool of filament. Fit it between the printer and the wall socket, run one ordinary print, and read the kilowatt-hour total off it when the print finishes.
One reading like that replaces every estimate on this page. It is your machine, printing your material, at the bed temperature you use, in the room you keep it in — measured rather than inferred. Do it once and the electricity term stops being a guess forever.
The cost calculator will take your measured figure directly. The method guide shows the arithmetic in full, and the regional rate table has the price side if you do not have a bill handy.
Why this input in particular gets forgotten
There is a general pattern behind it, and it is worth naming because it applies to the other overlooked costs too. What makes a cost easy to ignore is not how small it is — it is whether anything ever puts it on a screen.
Filament gets counted because the slicer volunteers a figure for it. The meter reading, the scrap rate, the wear on the machine and the hour of your evening are all invisible by default, and invisible costs do not get optimised, priced into quotes, or even noticed when they change. A printer that quietly started failing one print in five is a much larger financial event than a fifteen percent rise in filament prices, and only one of those two shows up on a receipt.
So the argument here is not that electricity is expensive. For most hobby printing it is not. The argument is that a cost you have never computed is a cost you cannot reason about, and it takes about ten minutes to move it from that category into the other one.