Element calculator
This calculator sizes the resistance heating elements for an electric kiln, a test kiln or a small furnace. You give it a supply voltage, a target power and the chamber dimensions; it returns the wire diameter, the coil geometry, the total wire to buy and the surface load, checked against the limits in the Kanthal handbook.
How do you size heating elements for an electric kiln?
The chain is short and every link is Ohm's law. You know the supply voltage and the power you want, so you know the total resistance the elements must present. Split that across however many elements run in parallel, and you have the resistance each one needs when hot.
Wire resistance is resistivity times length divided by cross-sectional area, so choosing a diameter fixes the resistance per metre, and the length follows. The catch is that resistivity climbs with temperature: Kanthal A-1 is not the same resistance at 1200 °C as it is on your bench. The tool applies the alloy's own temperature correction factor at the element's design temperature, not at room temperature, which is the difference between a kiln that reaches cone 6 and one that stalls short of it.
The last step is fitting that length of wire into the kiln. Wound into a coil of diameter D at pitch s, a length of wire becomes a much shorter stretched coil, and that coil has to fit the groove path in your walls. The tool draws the unwrapped wall strip so you can see whether it does.
What is wire surface load, and why do elements burn out?
Surface load, sometimes called watt density, is the power each element dissipates divided by the surface area of its wire, in watts per square centimetre. It is the single number that decides how long an element lasts, and it is the one most home-built kilns get wrong.
Kanthal alloys survive by growing a protective alumina layer on the wire surface. Run the wire too hard and it oxidises faster than that layer can reform. The element then sags, shorts against its neighbour or the wall, and fails inside a season. Run it gently and the same alloy fires for years.
The permissible load is not a fixed number: it falls as the furnace gets hotter. The tool interpolates the Kanthal curve for elements in grooves at your furnace temperature and shows how much margin you have. Thicker wire has more surface for the same power, so the usual fix for a load that is out of range is to go up a diameter and add length.
Which alloy: Kanthal A-1, APM or a nichrome?
Kanthal A-1 is the default for studio kilns, rated to 1400 °C element temperature, which leaves real margin over a cone 10 chamber. APM is the same family with better form stability and a slightly higher ceiling at 1425 °C, and it costs more. AF and D sit lower at 1300 °C and are chosen for particular handling and lifetime reasons rather than for top temperature.
The Nikrothal nichromes top out between 1100 and 1250 °C. They are tougher, more ductile and far more pleasant to wind and handle, and they do not become brittle after firing the way iron-chrome-aluminium alloys do. That last point matters more than it sounds: an aged Kanthal element can snap if you flex it cold. For cone 6 and below a nichrome is a reasonable choice, but check its permissible surface load, which is lower than Kanthal's at the same temperature.
How much element wire do I need to buy?
More than the coil length, and the difference is not small. Each element needs a lead-out at both ends: the tail that leaves the groove and reaches the terminal, doubled back on itself so it runs cooler than the working coil and does not burn off at the connection.
That lead-out is a fixed length per end, roughly 25 cm or 10 inches, set by how far the terminal is from the wall rather than by how long the element is. On a short test-kiln element it can be a noticeable fraction of the order. The wire-to-buy figure on this page already includes it for every element, so what you see is what to put in the basket.
Common questions
Can I use nichrome wire for a cone 6 kiln?
Not comfortably. Nikrothal 80 is rated to 1200 °C element temperature, and a cone 6 chamber sits at about 1220 °C with the element running hotter still, so the tool flags it over the alloy limit. Nichrome is more ductile and much easier to wind than Kanthal, and it does not go brittle with age, which makes it a good choice for earthenware and low-fire work up to around cone 1. For cone 6 and above, use a Kanthal grade.
Should elements be wired in series or in parallel?
Parallel splits the total power across elements, so each carries less current and can use thinner wire, and one failed element leaves the others working. Series puts the same current through everything and is simpler to wire. The calculator takes the parallel count as an input because it changes the resistance each element needs and therefore the wire diameter.
What are the D/d and s/d ratios?
D/d is the coil diameter divided by the wire diameter, and s/d is the pitch divided by the wire diameter. The Kanthal handbook recommends D/d between 5 and 12 and s/d between 2 and 4. Outside that range coils either sag under their own weight or radiate onto themselves and overheat. Auto-solve picks the thinnest wire whose surface load stays in range, then sets D and s to keep both ratios legal.
How long should kiln elements last?
An element run inside its surface-load limit should give hundreds of firings. One run over it can fail within a season. Lifetime is dominated by surface load and peak temperature, not by hours alone, so a kiln that spends time at cone 10 will get through elements considerably faster than one that lives at cone 6.
Keep going
- How the element calculator works Ohm's law through to the Kanthal design procedure, step by step.
- The controller reads 1222 °C, and the cone disagrees Element temperature, chamber temperature and what a cone measures are three different things.
- What 60 electric kilns tell you about power How much power studio kilns of this size actually carry, before you commit to a wire.
- Energy calculator Not sure what target power to enter? Work it out from the chamber and the insulation.
- Kiln builder Design the chamber the elements are going into.