Pottery Cone Temperature Calculator
Created by: Ethan Brooks
Last updated:
Convert between Orton pyrometric cone numbers and kiln firing temperature in Fahrenheit or Celsius, adjusted for slow, standard, or fast firing rates.
Pottery Cone Temperature Calculator
PotteryConvert between Orton pyrometric cone numbers and kiln temperature, adjusted for your firing rate.
What is a Pottery Cone Temperature Calculator?
Cone 6 matures at approximately 2232°F (1222°C) when fired at a standard rate of 270°F per hour, making it the most common firing temperature for mid-range stoneware and porcelain in electric kilns. A pyrometric cone is a small ceramic object formulated to bend and slump at a specific, repeatable combination of temperature and time, rather than at a single fixed temperature alone. This pottery cone temperature calculator converts between Orton cone numbers and kiln temperature in either direction, adjusting the result for whether your kiln fires slowly, at a standard rate, or quickly.
Potters rely on cones because a kiln pyrometer only reports the instantaneous air temperature near the sensor, which does not capture whether the ware itself has absorbed enough cumulative heat to fully mature. Cones solve this by physically responding to accumulated heat-work, bending over and touching the kiln shelf once the right combination of time and temperature has been reached. This is why the same cone matures at a slightly different peak temperature depending on how fast the kiln was ramping during the final approach to temperature.
This calculator uses the standard Orton cone chart, covering all 34 cones from 022, the coolest, through 13, the hottest, and adjusts each cone's reference temperature for slow, standard, or fast firing rates using heat-work offsets calibrated against published multi-rate Orton data. It works in both directions: enter a cone number to find its firing temperature, or enter a temperature reading to find the nearest matching cone.
Beyond the basic conversion, the calculator also reports the cone's firing category (low, mid, or high fire), which clay bodies and glaze types are typically formulated for that range, a recommended firing duration estimate, and the neighboring cones above and below for quick comparison, making it useful for planning a firing schedule as well as interpreting a finished one.
How the Pottery Cone Temperature Calculator Works
Pyrometric cones do not respond to peak temperature in isolation, they respond to heat-work, the combined effect of time and temperature accumulated as the kiln approaches its target. A cone fired slowly spends more total time exposed to high temperatures on its way up, so it absorbs more heat-work at any given temperature than the same cone fired quickly would. As a result, a slow firing reaches full cone maturity at a lower peak temperature than a standard firing, while a fast firing needs a higher peak temperature to deliver the same amount of heat-work in less time.
This calculator looks up each cone's standard-rate reference temperature from the Orton cone chart, then applies a heat-work adjustment factor based on your selected firing rate to estimate the actual peak temperature needed. In reverse mode, it applies the same adjusted values across all 34 cones and finds the closest match to your entered temperature for the selected rate.
Cone Temperature Formulas
Adjusted temperature = Standard cone temperature x (1 + rate offset)
Slow rate offset ≈ -1.8%, Standard rate offset = 0%, Fast rate offset ≈ +1.2%
Celsius = (Fahrenheit - 32) x 5/9, Fahrenheit = Celsius x 9/5 + 32
Nearest cone (reverse mode) = cone with adjusted temperature closest to entered temperature
Example Calculations
Example 1: Cone 6 at standard vs. slow rate
Cone 6 fired at the standard rate of 270°F/hr matures at 2232°F (1222°C), the most common target for electric kiln stoneware and porcelain glazes. The same cone fired slowly at 108°F/hr matures at a lower peak of roughly 2192°F, since the extended time at high temperature delivers more cumulative heat-work, letting the cone bend sooner on the temperature scale. A potter switching from a fast glaze schedule to a slower one should expect the kiln to shut off around 40°F earlier to hit the same cone 6 result, which matters when programming a digital kiln controller by temperature alone.
Example 2: Cone 06 bisque firing
Cone 06 is the standard bisque firing target, maturing at 1798°F (981°C) at a standard rate. Bisque firings are often run a bit slower through the water-smoke stage, below about 1100°F, to safely drive off residual moisture and any remaining organic material before the clay densifies, which this calculator accounts for when you select the slow firing rate. At a slow rate, cone 06 matures closer to 1765°F, while a fast bisque schedule would need to climb a little higher, near 1820°F, to deliver the same heat-work in less total time.
Example 3: Cone 10 reduction firing
Cone 10 matures at 2345°F (1285°C) at a standard rate, the classic target for high-fire stoneware and porcelain reduction glazes like celadons, shinos, and tenmokus. Because cone 10 firings often run long and slow to develop reduction effects and allow glazes to fully melt and settle, the slow rate setting shows a meaningfully lower required peak temperature than the standard chart value, often more than 40°F lower. This is one reason experienced gas-kiln potters trust witness cones over a pyrometer reading alone when judging whether a long reduction firing has truly finished.
Common Pottery Applications
- Look up the firing temperature for a glaze or clay body's recommended cone before programming a kiln controller, so you do not have to dig through a printed chart mid-project.
- Convert a kiln controller's peak temperature reading into the nearest equivalent cone to sanity-check a firing program before committing a full load of finished work to the kiln.
- Compare how firing rate changes the actual peak temperature needed to mature the same cone, useful when switching between a slow candling bisque schedule and a faster glaze schedule.
- Identify which clay bodies and glaze types are appropriate for a target cone before buying materials, avoiding mismatched purchases for a planned firing temperature.
- Plan an approximate firing duration for a kiln load based on the target cone and firing rate when scheduling studio time or a shared community kiln.
- Check the next cone up or down to understand how much temperature margin exists before over-firing or under-firing a load of glazed or bisque ware.
- Cross-reference Fahrenheit and Celsius cone temperatures when following recipes, glaze chemistry references, or kiln manuals written for a different regional unit system.
Tips for Better Pottery Results
Always confirm firing results with physical witness cones placed where they are visible through a kiln peephole, rather than relying on a digital pyrometer reading alone. A pyrometer only reports instantaneous temperature at one point in the kiln, while a witness cone reflects the actual accumulated heat-work the ware has received, which is what determines whether clay and glaze have truly matured.
Use a slightly slower firing rate, especially during the final approach to peak temperature, for thick-walled or densely packed loads, since heat needs more time to penetrate evenly throughout the kiln. This calculator's slow rate setting reflects the lower peak temperature such a schedule will actually need to reach the same cone.
Remember that this calculator estimates standard reference behavior; always check the specific cone manufacturer's published chart and your kiln manufacturer's recommendations, since cone batches, kiln atmosphere, and shelf placement can all shift the effective maturing temperature slightly.
Frequently Asked Questions
What temperature is cone 6 in pottery?
Cone 6 matures at approximately 2232°F (1222°C) at a standard firing rate of 270°F per hour. This is the most common firing temperature for mid-range stoneware and porcelain glazes in electric kilns. At a slower firing rate the same cone bends at a slightly lower peak temperature, and at a faster rate it requires a slightly higher peak temperature to fully mature.
What's the difference between cone 6 and cone 10?
Cone 6 matures around 2232°F (1222°C) while cone 10 matures around 2345°F (1285°C), a difference of roughly 113°F. Cone 6 is considered mid-fire and is common for electric kiln oxidation firing, while cone 10 is high-fire and traditionally associated with reduction firing in gas kilns, producing different clay and glaze characteristics including denser vitrification and different glaze chemistry results.
Does firing rate really change the temperature needed?
Yes. Pyrometric cones respond to accumulated heat-work, the combination of time and temperature, not just peak temperature. A slow firing delivers more total heat-work at a given temperature than a fast firing does, so a cone fired slowly will bend at a slightly lower peak temperature than the same cone fired quickly. This calculator adjusts the standard chart temperature based on your selected firing rate.
What is a witness cone and why use one?
A witness cone is a small pyrometric cone placed inside the kiln, visible through a peephole, that physically bends when it has absorbed enough heat-work to mature. Unlike a digital pyrometer, which only reports instantaneous temperature, a witness cone confirms that the ware has actually received enough cumulative heat-work to fully mature the clay and glaze, making it the most reliable way to judge firing completion.
How do I convert a kiln temperature reading to a cone number?
Select "Temperature to Cone" mode, enter your kiln pyrometer reading and the firing rate you used, and the calculator finds the nearest Orton cone equivalent. Keep in mind a pyrometer reading is only a temperature snapshot, while the actual cone result also depends on how long the kiln held near that temperature, so witness cones remain the more reliable confirmation.
Why do small cone number prefixes like 06 mean a lower temperature than 6?
Orton cone numbering uses two separate sequences. Cones prefixed with a leading zero, such as 022 down to 01, run from coolest to hottest as the number decreases, covering low-fire temperatures. Cones without a leading zero, 1 through 13, continue the sequence upward into mid and high-fire territory, with larger numbers meaning hotter temperatures.
Can I use this calculator for both Celsius and Fahrenheit?
Yes. Choose your preferred temperature unit from the dropdown and all results, including the chart and reference table, will display in that unit. The underlying calculation always uses the Orton cone chart's Fahrenheit reference values internally for accuracy, then converts for display.
Sources and References
- Edward Orton Jr. Ceramic Foundation. "Orton Pyrometric Cone Chart." Orton Ceramic Foundation, 2023.
- Hamer, Frank and Janet. The Potter's Dictionary of Materials and Techniques, 5th Edition. A&C Black, 2004.
- Hesselberth, John and Roy, Ron. Mastering Cone 6 Glazes, 2nd Edition. Glazemaster Press, 2002.
- Digitalfire Corporation. "Orton Cone Chart and Heat-Work Reference." Digitalfire Reference Library, 2023.
- Rhodes, Daniel. Kilns: Design, Construction, and Operation, 2nd Edition. Chilton Book Company, 1981.