Earth Oven Sizing Calculator
Calculate dome dimensions, door size, thermal mass, heat-up time, and cooking capacity for a cob/clay pizza and bread oven.
About this calculator
An earth oven (cob or clay pizza oven) is fired directly inside its dome; once the walls have soaked up enough heat, the coals are raked out and food bakes from stored radiant heat alone. This calculator follows the proportions popularized by Kiko Denzer's "Build Your Own Earth Oven": interior dome height is set at 67% of interior diameter, door height at 63% of dome height, and door width at half the interior diameter — ratios chosen so the door is small enough to hold in heat but tall enough to draft properly during firing. Floor area (a simple circle from your interior diameter) drives cooking capacity: pizza count assumes 30 cm pies with 30% spacing between them, and it can also reverse-solve for the diameter needed to fit a target number of pizzas at once.
Thermal mass is the weight of the dense cob shell itself, computed as the volume between the outer and inner dome hemispheres times cob's density (1800 kg/m³) — this is the mass that actually stores your firing heat. Heat-up time comes from the energy needed to raise that thermal mass to roughly 350°C (using cob's specific heat, ~0.93 kJ/kg·°C) divided by an estimated fire power that scales gently with oven size. Real heat-up times vary with wood quality, wall moisture in a newly built oven, and how the fire is tended, so treat the estimate as a starting point — most builders find 1.5–2 hours realistic for a well-cured oven at typical sizes.
Inputs
Results
Interior dome height
60 cm
≈ 7 credit cards
How to Use This Calculator
- Enter the desired interior dome diameter in centimeters.
- Set wall thickness, insulation layer thickness, and the number of pizzas to cook simultaneously.
- The calculator returns dome height, door dimensions, outer diameter, maximum pizza capacity, and thermal mass.
- Use the heat-up time estimate to plan your firing schedule (typically 1.5–2 hours before cooking).
- Adjust diameter to trade between pizza capacity and build materials required.
How the result changes with Interior dome diameter
| Interior dome diameter | Interior dome height |
|---|---|
| 45 | 30 cm |
| 68 | 46 cm |
| 135 | 90 cm |
| 200 | 134 cm |
What each input means
- Interior dome diameter
- Inner diameter of the oven floor. 60–75 cm for personal use, 90–120 cm for family/entertaining.
- Dense cob wall thickness
- Thickness of the inner dense clay/cob thermal layer. 10–15 cm is typical.
- Insulation layer thickness
- Outer insulation layer (sawdust-clay, perlite, or vermiculite mix). 5–10 cm recommended.
- Pizzas at once
- How many 30 cm (12 in) pizzas you want to bake simultaneously.
What each result means
- Interior dome height
- Height of the dome interior from floor to apex.
- Door height
- Optimal door opening height (63% of dome height for proper draft).
- Door width
- Door opening width (50% of interior diameter).
- Overall outer diameter
- Total footprint diameter including walls and insulation.
- Max 30 cm pizzas
- Maximum number of 12-inch pizzas that fit simultaneously.
- Max bread loaves
- Approximate 1 kg bread loaves that fit on the oven floor.
- Thermal mass (cob layer)
- Weight of the dense inner cob dome layer.
- Heat-up time
- Approximate firing time to bring the oven to pizza temperature (~350 °C).
- Recommended diameter for pizza count
- Interior diameter needed to fit your desired number of pizzas.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersInterior dome diameter = 90, Dense cob wall thickness = 12, Insulation layer thickness = 7, Pizzas at once = 2 = 4 input(s) provided
- Calculate Interior dome heightInterior dome height = interiorDiamCm * 0.6760 = 60
- Calculate Door heightDoor height = domeHeightCm * 0.6338 = 38
- Calculate Door widthDoor width = interiorDiamCm * 0.545 = 45
Engine last updated . Checked against 1 independently-derived test — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does the calculator use 67% for dome height when the intro mentions 60–75%?
The engine settles on a single fixed ratio of 67% of interior diameter for dome height — landing in the middle of the traditional 60–75% range used across earth-oven building guides — rather than exposing it as an adjustable input. Door height and width then derive from that computed dome height (63%) and the interior diameter (50%), so all three dimensions move together whenever you change the interior diameter.
How does the 'recommended diameter' output relate to my pizza count?
It works backward from your target pizza count: each 30 cm pizza is assumed to need its own circular footprint plus 30% spacing, so the calculator multiplies that per-pizza area by your desired count and solves for the interior diameter of a circle large enough to hold them all. If you build to the diameter you entered instead, compare it against this recommended value to see whether your oven will actually fit that many pizzas at once.
Why does adding insulation thickness increase the outer diameter but not the heat-up time?
Outer diameter directly adds twice the insulation thickness to the interior diameter plus wall thickness, since insulation is an outer shell wrapped around the structure. Heat-up time, however, is driven only by the thermal mass of the dense inner cob layer and an estimated fire power — insulation reduces heat loss *after* firing (helping the oven hold temperature longer for cooking) but isn't part of the heat-up energy calculation itself.
What is 'thermal mass' actually measuring here, and why does it matter?
Thermal mass is the calculated weight of the dense cob shell alone (the volume between the outer and inner dome hemispheres times cob's density of 1800 kg/m³) — it excludes the outer insulation layer entirely. This is the mass that has to be heated to roughly 350°C during firing and that then radiates heat back out to cook food, so a larger thermal mass means a longer heat-up time but also longer retained cooking heat afterward.
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