A kiln controller runs a program of segments — climb at so many degrees an hour to a temperature, then climb at a different rate to the target, then hold. Every segment is a division: degrees to cover over degrees per hour. Add the segments and the hold, and you know whether the glaze load finishes at 9 p.m. or 2 a.m., which decides whether anyone is around to unload it.
A cone 06 bisque from 70°F: 150°/hr to 250°F, then 250°/hr to 1,945°F, with a 10-minute hold, is 8.15 hours.
The example
Three common studio programs. The slow first ramp is the candling stage that drives water out before it turns to steam inside the clay.
| A | B | C | D | E | F | G | H | |
|---|---|---|---|---|---|---|---|---|
| 1 | Program | Start | Seg 1 to | Rate 1 | Target | Rate 2 | Hold (min) | Hours |
| 2 | Cone 06 bisque | 70 | 250 | 150 | 1945 | 250 | 10 | 8.15 |
| 3 | Cone 6 glaze | 70 | 250 | 150 | 2232 | 200 | 15 | 11.36 |
| 4 | Cone 04 fast | 70 | 180 | 100 | 1828 | 300 | 0 | 6.59 |
The formula
Each segment is its own division, added together with the hold converted to hours:
How it works
Break the firing into the pieces the controller sees:
(C2-B2)/D2is segment 1: the degrees from start to the first setpoint, divided by the rate in degrees per hour. From 70 to 250 at 150°/hr is 1.2 hours.(E2-C2)/F2is segment 2: from the first setpoint to the target at the second rate. 250 to 1,945 at 250°/hr is 6.78 hours.G2/60converts a hold in minutes to hours so the units match. A 10-minute soak is 0.17 hours.- Add a third segment the same way for a three-step program, and wrap the whole thing in
ROUND(...,2)so the schedule column does not show eleven decimals.
Add the result to the load time with =LoadTime+Hours/24 to get a finish time you can put on the studio calendar — and remember the kiln needs 12 or more hours to cool before anyone opens it.
Try it: interactive demo
Enter the start and setpoint temperatures, the two ramp rates, and the hold.
Variations
Finish time on the calendar
Excel stores a day as 1, so divide hours by 24 and add to the load date-time. Format the cell as a date and time.
Three-segment program
Just keep adding segments. A slow final approach to the cone is common on glaze firings.
Pitfalls & errors
Controllers cannot always hit the programmed rate near the top. An old element set may climb at 100°/hr when the program says 200, so a mature kiln finishes later than this formula predicts. Log actual finish times and adjust the rates you enter.
Use the same units throughout. A program written in °C with rates in °F/hr gives a very confident, very wrong answer — the formula cannot tell the difference.
Do not put the hold in hours in one row and minutes in another. Pick minutes, label the column, and convert inside the formula every time.
Practice workbook
Frequently asked questions
Why is the first ramp so slow?
Can I use this for cooling time too?
Stop fighting formulas. Learn them in a day.
This recipe is one of hundreds of real-world formulas we teach. Our Excel Formulas & Functions class covers lookups, logic, text, and dynamic arrays hands-on — live in Dallas–Fort Worth, Houston, Austin, Oklahoma City, Denver, or online.
See the Formulas & Functions Class