Witness Cone Pack & Temperature Calculator
Select a cone to build a guide-target-guard pack, or start with a temperature to find the nearest published Orton cone. The result uses the cone form and the heating rate during the final part of the firing.
Recommended witness cone packCone 5½ (guide) · Cone 6 (target) · Cone 7 (guard)
- Target cone equivalent temperature (°C)
- 1,222
- Guide cone and temperature
- Cone 5½ at 1,203 °C
- Guard cone and temperature
- Cone 7 at 1,239 °C
- Nearest cone
- Cone 6 (selected target)
- Cone bracket
- Cone 5½ at 1,203 °C to Cone 7 at 1,239 °C.
- Table applicability
- Orton publishes 38 of 38 supported cone temperatures for self-supporting cones at 60°C/hr.
Temperatures are Orton reference equivalents for the final 100°C of firing, not controller setpoints.
No soak, atmosphere, mounting-height, or kiln-load adjustment is applied.
How to use this calculator
- Choose cone number to build a pack, or target temperature to work backward from a temperature reading.
- Select Celsius or Fahrenheit for the temperature you enter and the temperatures shown.
- Choose the physical cone form and the average rise during the final 100°C or 180°F of firing.
- For a cone lookup, use the guide, target, and guard together as a witness pack on the shelf.
How the witness cone pack is selected
A witness pack has three consecutive pyrometric cones: a cooler guide, the target cone, and a hotter guard. The guide shows whether the firing approached the target, the target shows the intended heatwork, and the guard shows whether the firing went beyond it. This calculator keeps the physical Orton order, including the important transition from cone 01 to cone 1 and the half cones between 06 and 05 and between 5 and 6.
Let the ordered cone sequence be C = [022, 021, …, 06, 05½, 05, …, 01, 1, 2, …, 14], from coolest to hottest. For a target cone C[i], the pack is guide = C[i − 1], target = C[i], and guard = C[i + 1]. Cone 022 has no cooler guide in this sequence, and cone 14 has no hotter guard.
How the temperature lookup works
Each temperature is read from Orton's published table for the selected cone form and final-zone heating rate. The calculator stores the table in Celsius. When Fahrenheit is selected, it converts the selected table value with F = (C × 9 ÷ 5) + 32; converting an entered Fahrenheit temperature back uses C = (F − 32) × 5 ÷ 9.
In temperature-to-cone mode, it finds the published entry with the smallest absolute difference: nearest cone = arg min |T(cone, form, rate) − target temperature|. It then reports the closest published temperature at or below the target and the closest one at or above it. At an exact match, the difference is zero. Outside a selected table's range, the calculator reports the nearest endpoint rather than pretending there is a two-sided bracket.
Why form and rate matter
Cones respond to heatwork, not an instantaneous air temperature. A self-supporting cone, a large cone mounted in a plaque, and a small kiln-sitter cone bend under different published conditions, so their table values are not interchangeable. The rate is the average rise in the final 100°C or 180°F, where the cone is maturing; it is not the average rate for the whole firing. Orton publishes self-supporting values at 15, 60, and 150°C per hour, large regular values at 60 and 150°C per hour, and small regular values at 300°C per hour. Blank cells remain unavailable here.
What this calculation does not model
This is a table lookup, not a kiln controller. It does not estimate the effect of a hold, reduction or other atmosphere, cone mounting height, kiln loading, shelf-to-shelf variation, thermocouple error, or a different cone manufacturer. A hold adds heatwork and can bend a cone farther at the same displayed controller temperature, so do not treat the equivalent temperature as a universal shutoff point.
Worked example
For a self-supporting cone 6 fired at 60°C per hour during the final 100°C, Orton's table gives 1,222°C. The calculator selects cone 5½ as the guide at 1,203°C, cone 6 as the target at 1,222°C, and cone 7 as the guard at 1,239°C. In Fahrenheit, the target equivalent is (1,222 × 9 ÷ 5) + 32 = 2,231.6°F.
Starting instead with 1,222°C under those same selections returns cone 6 as an exact match. It does not interpolate a new cone or adjust for a hold.
Common questions
Which three witness cones should I use for a cone 6 firing?
Use the immediately adjacent cones in physical melting order: cone 5½ as the guide, cone 6 as the target, and cone 7 as the guard. Match all three to the same cone form and use them where they can be seen in the ware setting.
Why are cone 06 and cone 6 different?
Leading zeroes are significant. Cone 06 is a low-fire cone, while cone 6 is a much hotter mid-fire cone; the sequence runs from cone 01 directly to cone 1. Treating them as ordinary decimal numbers would put them in the wrong order.
Why does one cone have several equivalent temperatures?
The table temperature depends on the cone form and the rate of rise near maturity. A faster final climb needs a higher air temperature for the same cone bend, while a slower climb gives the cone more time to absorb heatwork.
Can kiln-sitter cones be used as shelf witness cones?
Small regular cones have a published 300°C-per-hour table and are normally used in kiln sitters. They can be used where space is limited only when mounted and read according to the manufacturer’s instructions; they are not interchangeable with self-supporting shelf cones.
How many cone packs should I place in a kiln?
Use enough packs to check the areas that matter, commonly more than one shelf and locations that may fire differently. Place each pack where it can be viewed safely and represents the ware, then compare the physical bends after firing.