What this calculator does
Online kiln calculators usually stop at the cost of one firing. But if you sell your pots, the number you actually need is the cost per piece — and almost every functional piece is fired twice: a bisque firing to harden the clay, then a glaze firing to mature the glaze. This tool works out the electricity cost of each firing, divides it across how many pieces share that load (bisque and glaze loads hold different numbers), and adds the two shares so you see the true firing-energy cost of a single mug, bowl or vase.
How to use it
- Pick your currency and enter your electricity rate per kWh from a recent bill.
- Enter your kiln's power rating (kW or W — it's on the data plate) and the duty cycle.
- For the bisque firing, enter how many hours it runs and how many pieces fit in that load.
- Do the same for the glaze firing — glaze loads usually hold fewer pieces because glazed work can't touch.
- Choose how many firings each piece goes through, and an optional surcharge buffer.
The per-piece figure and breakdown update instantly as you type.
The formula
The cost of a single firing follows the standard electric-kiln formula used across the trade:
kW × firing hours × rate per kWh × duty cycle = cost of one firing
This calculator then takes the extra steps the per-firing calculators skip:
- Bisque share = bisque firing cost ÷ pieces in the bisque load
- Glaze share = glaze firing cost ÷ pieces in the glaze load
- Per-piece cost = the shares for the firings that piece actually receives (bisque, glaze, or both)
- Surcharge = per-piece cost × (1 + buffer %)
Worked example
A 7.4 kW kiln, 50% duty cycle, $0.16/kWh. A 9-hour bisque holding 40 pieces costs about 7.4 × 9 × 0.16 × 0.5 = $5.33, or roughly $0.13 per piece. An 11-hour glaze holding 24 pieces costs about 7.4 × 11 × 0.16 × 0.5 = $6.51, or about $0.27 per piece. A mug fired both times carries roughly $0.40 in firing electricity — small, but real once you multiply it across hundreds of pieces a year.
Why firing cost per piece matters when you sell
- Pricing accuracy: a per-piece firing line slots straight into your costing alongside clay, glaze and labour.
- Form choices: tall narrow forms pack tighter than wide bowls, so their per-piece share is lower — handy when deciding what to make in volume.
- Pack discipline: half-empty firings double the cost each piece carries; the calculator shows that instantly when you lower the piece count.
Common mistakes
- Forgetting the second firing. Costing only the glaze (or only the bisque) understates every piece — most are fired twice.
- Using full kiln wattage continuously. Elements cycle on and off; ignoring the duty cycle roughly doubles your estimate.
- Using the same piece count for both loads. Bisque packs denser than glaze, so they almost always differ.
- Mistaking this for total cost. It's firing energy only — not the finished cost of a pot.
FAQ
How do I work out the firing cost per pottery piece?
First find the cost of one firing: kiln kilowatts × firing hours × your electricity rate per kWh × duty cycle (around 50% for most electric kilns). Then divide that firing cost by the number of pieces that fit in that load. Because most pottery is bisque fired once and glaze fired once, add the bisque cost-per-piece to the glaze cost-per-piece to get the real per-item firing cost. This tool does all of that automatically and keeps the two loads separate, since a bisque load usually holds more pieces than a glaze load.
What duty cycle should I use for an electric kiln?
A kiln's elements switch on and off to hold the climb rate, so they aren't drawing full power for the whole firing. Across typical electric cone-fire programs, a duty cycle of roughly 50% is a widely used estimate. Slow programs that push near the kiln's maximum temperature tend to run higher; long hold segments run lower. If your controller reports actual element-on time at the end of a firing, use that exact figure instead of the estimate for a tighter number.
Does each piece really get fired more than once?
Usually yes. Most functional pottery is bisque fired once to harden it, then glaze fired once to mature the glaze — so a single mug carries a share of two separate firings. This calculator adds both shares together by default. If your process adds extra firings, such as a third firing for lustre or decals, switch the per-piece setting or treat that work separately so the cost reflects every kiln run it goes through.
Is this the full cost of making a pot?
No. This tool isolates the electricity cost of firing only. It doesn't include clay, glaze materials, your labour, kiln element and shelf wear, studio rent or packaging. Treat the per-piece figure as the firing-energy line of your costing, then add your other costs before setting a retail price. The suggested surcharge is a guide for recovering firing energy with a small buffer — not a complete price.
Why split bisque and glaze loads separately?
Because they hold very different numbers of pieces. In a bisque firing the clay is unglazed, so pieces can touch and even nest, packing the kiln densely. In a glaze firing the molten glaze would fuse anything that touches, so pieces need clear space and a load holds noticeably fewer. Using one combined count would misallocate cost. Entering each load's own piece count gives a fairer per-piece share.