Nameplate power is a ceiling, not a rate
The arithmetic underneath a firing cost is trivially simple: kilowatt-hours equal kilowatts multiplied by hours, and cost is kilowatt-hours multiplied by your rate. Everything difficult about the estimate sits in the kilowatts, because a kiln does not draw its rated power for the duration of a firing.
Elements are switched on and off by the controller to follow the programmed ramp. Early in a firing, climbing from room temperature at a modest rate, the kiln has more power available than it needs and cycles. In the middle, climbing hard toward top temperature, it may be at or near full power continuously because it cannot climb any faster. At a hold, it is only replacing what leaks out through the walls, and the duty drops sharply. Averaged across a typical cone 6 firing, a kiln commonly draws well under its nameplate.
That is why this page asks for a duty factor per segment rather than assuming one. A calculation that multiplies nameplate kilowatts by total hours will overstate the cost substantially, and a calculation that applies one flat percentage across the whole firing will get the shape wrong even if the total happens to land close.
Getting duty factors you can trust
The honest answer is to measure. A plug-in energy meter is inexpensive for a 120 V kiln, and for a hard-wired 240 V kiln an electrician can fit a circuit-level monitor or you can read the meter itself before and after a firing with nothing else running. One firing gives you a total kilowatt-hour figure, and dividing that by the hours gives your real average draw. That number, once you have it, is worth more than any estimate on this page.
| Phase of the firing | What the kiln is doing | Duty tends to be |
|---|---|---|
| Low ramp, candling or slow start | Barely working, holding a slow climb | Low |
| Mid climb | Following a moderate ramp with power to spare | Moderate to high |
| Final climb to top temperature | Often at or near everything it has | Highest |
| Hold or soak | Replacing wall losses only | Low |
| Controlled cool | Slowing a fall, not driving a rise | Low, and often zero |
Several things shift the whole picture upward. Elements degrade with age and a worn set draws less current, which means the kiln takes longer to reach the same temperature and may fail to reach it at all near the end of its life — longer hours at similar power costs more, not less. A heavy load of dense ware absorbs more heat than a light one. A cold garage in winter loses more through the walls than a heated room. Thin or damaged insulating brick leaks continuously.
What the rate should be
Use your all-in cost per kilowatt-hour, taken from a bill by dividing the total amount by the kilowatt-hours used, not the headline supply rate. Delivery charges, distribution charges and taxes often add a substantial fraction on top of the energy price, and on some bills they are larger than the energy component. If you are on a time-of-use tariff, a kiln is a large enough load that when you start it matters: a firing that runs overnight on an off-peak rate can cost meaningfully less than the same firing started in the afternoon, and the controller's delay-start function exists partly for this.
The per-piece figure at the bottom is worth treating carefully if you are pricing work. It divides one firing across the load, so it rewards packing the kiln full and punishes firing three mugs. That is real, but it is also only the energy. Elements, thermocouples, shelves, kiln wash and the clay itself are not in it, and neither is your time.
Bisque and glaze are different firings
A bisque is typically a slow climb to a lower temperature with a long, gentle early phase to drive off water and burn out organics, and it often takes longer in hours than a glaze firing while using less energy overall because the top temperature is lower. A glaze firing goes higher, frequently faster, and may include a hold at top temperature and a controlled cool afterwards, both of which add hours. Model them separately rather than averaging, and if you fire a piece through both, add the two results together to get the true energy in the finished work.
Once you know what a firing costs, the other half of the studio arithmetic is the material. The glaze batch calculator handles the recipe side, and clay shrinkage determines how much fits on a shelf in the first place.
Questions people ask
How much does one kiln firing cost?
For a mid-size studio kiln, expect something in the range of a few dollars to a couple of tens of dollars per firing, and that spread is wide enough that only your own numbers are useful. What sets it is the kiln power, the top temperature, the hours, and above all your electricity rate, which varies by several times across regions. A 7 kW kiln firing for twelve hours at an average 60 percent duty uses about 50 kWh; the same firing costs three times as much in one place as in another purely because of the tariff. Fill in your own rate from the bill rather than trusting a figure quoted in a workshop.
What duty factor should I use?
Measure it rather than guess it, because it is the one input on this page that can be off by a large margin. A kWh meter on the circuit for a single firing gives you a total, and dividing that by the hours gives your real average draw as a fraction of nameplate. If you have to estimate for now, note the shape rather than a single number: climbing hard toward top temperature uses close to everything the kiln has, a gentle early ramp uses far less, and a hold uses only what leaks through the walls. The defaults here are placeholders that produce a plausible total for a typical kiln, not measurements of yours.
Does a fuller kiln cost more to fire?
It uses somewhat more energy per firing and considerably less per piece. More ware means more thermal mass to bring up to temperature, so the elements work harder and the firing may run slightly longer, but the large fixed cost of heating the kiln structure and replacing wall losses is the same whether the shelves are full or nearly empty. This is why the per-piece figure moves so much with the load count. It is also why firing a nearly empty kiln is the most expensive thing a studio does, and why people wait to accumulate a load even when it delays work.
Do old elements use more electricity?
Not more power at any instant — a worn element has higher resistance and draws less current, so the kiln is weaker rather than hungrier. What happens is that the firing takes longer to reach the same temperature, and a longer firing at a similar draw is more kilowatt-hours in total. Late in element life the kiln may struggle to reach top temperature at all, sitting at high duty for hours near the end and using a great deal of energy without ever getting there. If firings have been creeping longer and cones are dropping later, that is the usual explanation, and the fix is elements rather than a longer hold.
Is it cheaper to fire overnight?
Only if your tariff has time-of-use pricing, in which case yes and often substantially, since a kiln is one of the largest loads a household has. The energy used is identical; only the price per kilowatt-hour changes. Check the bill for whether a time-of-use structure applies, and note that many kiln controllers have a delay-start specifically so a firing can be shifted into a cheaper window. Set against that, an unattended overnight firing means nobody is present if something goes wrong, and that trade-off is a judgement about the kiln, the space and what the manufacturer says about unattended operation rather than about the tariff.