To find out the cost of a single firing in an electric kiln, you need to know the wattage of the kiln, measured in kilowatts. If you multiply the kiln wattage by the cost of electrical energy per kilowatt-hour, you will know how much the kiln costs to run each hour. In 2010, average prices per kwh ranged from 10 to 17 cents. So an 11-watt kiln would cost between $1.10 and $1.87 for every hour of firing.
Gas kilns are typically less efficient in terms of fuel burning. However, because gas is cheaper than electricity, the actual cost of running similar-sized kilns is similar whether the kiln runs on electricity or gas.
The efficiency of a kiln increases as the kiln size and volume increases. In a cube-shaped kiln, the ratio of the kiln's external surface area (which loses heat) and its internal volume decreases. This, in turn, increases the efficiency of the kiln.