Kiln Load Calculator
How many pieces fit in a firing and what each one costs — a half-full kiln doubles the cost of everything in it.
A simple grid pack, so real loading beats it — pots nest, small things go between larger ones, and a bisque can stack in ways a glaze firing cannot. Treat the capacity as a floor rather than a target. Nothing is uploaded.
A half-full kiln doubles the cost of every piece in it
A firing is a fixed cost. The elements draw what they draw to reach cone whether there are 64 pots inside or one, so the electricity divides across whatever happens to be in there. That makes cost per piece a hyperbola, not a line: this kiln holds 64 mugs at $14 a firing, so a full load is $0.22 each and a half load is $0.44.
| Pieces in the load | How full | Cost each | Against a full load |
|---|---|---|---|
| 64 | 100% | $0.22 | 1.0× |
| 48 | 75% | $0.29 | 1.3× |
| 32 | 50% | $0.44 | 2.0× |
| 16 | 25% | $0.88 | 4.0× |
| 4 | 6% | $3.50 | 16.0× |
| 1 | 2% | $14.00 | 64.0× |
Which sounds obvious stated plainly and is routinely ignored, because the pressure to fire is about having work ready rather than about having the kiln full. Firing four pieces costs $3.50 each — sixteen times the full-load rate — and firing one costs the entire $14. The cost times the count is always the firing cost, which is the whole relationship in one line.
Shelves and posts eat more height than you would think
Every level costs the height of the piece plus the shelf plus the clearance
the posts hold — here 10 + 1.5 + 2.5 =
14 cm, of which
29% is not pot at all. So the
60 cm interior takes 4 levels, not the
6 that dividing by the mug height would suggest.
The overhead is fixed per level, so it hurts short work most. A kiln full of mugs loses a
quarter of its height to furniture; the same kiln full of vases loses almost none. That is
also the argument for firing mixed heights together where the glaze schedule allows it —
the tall pieces pay for the shelf the short ones would have needed anyway.
How to use
- Enter the kiln interior and shelf dimensions.
- Add the shelf thickness and the clearance the posts hold.
- Enter the piece size and what a firing costs.
- Read the capacity and the cost per piece at your load.
Frequently asked questions
Does firing a smaller load cost less?
Less in total, and far more per piece. A firing is a fixed cost — the elements draw what they draw to reach cone whether the kiln is full or not — so the cost divides across whatever is inside. A half-full kiln doubles the cost of every piece in it, and firing one piece costs the whole firing.
How much does a nearly empty firing cost?
On the example here, a full load is 22 cents a mug and four pieces is $3.50 each — sixteen times the rate. The cost times the count is always the firing cost, which is the entire relationship in one line.
How many levels will fit?
Fewer than dividing the height by the pot suggests. Each level costs the piece plus the shelf plus the clearance the posts hold, so 10 cm mugs in a 60 cm kiln take four levels rather than six once 4 cm of furniture per level is counted.
Why does that matter more for small work?
Because the overhead is fixed per level. A kiln full of mugs loses a quarter of its height to shelves and posts; the same kiln full of vases loses almost none. It is also the argument for firing mixed heights together where the schedule allows — the tall pieces pay for a shelf the short ones would have needed anyway.
Is a grid the right way to pack?
It is a floor, not a target. Real loading beats it easily — pots nest, small things go between larger ones, and a bisque can stack in ways a glaze firing cannot. Use the number as a conservative capacity rather than a limit.
Should I wait to fill the kiln?
That is what the arithmetic argues, and it is not the whole decision. Work that is dry and waiting takes up space and risks damage, deadlines exist, and a bisque holding up a glaze firing costs more than electricity. The calculator tells you the price of firing early; whether to pay it is yours.
What should I put for the cost of a firing?
Kilowatt-hours times your rate is the starting point, and element and thermocouple wear is a real addition — elements are consumable and a firing spends some of them. Whatever figure you use, it is fixed per firing, which is the only property this calculation depends on.
Does this send anything anywhere?
No. Every figure is computed in your browser, and nothing is uploaded or stored.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.