Pottery Coil Building Height Calculator

How Pottery Coil Building Height Is Calculated

Coil building is one of the oldest pottery techniques, dating back over 25,000 years. Each coil adds a predictable amount of height depending on its diameter (thickness) and the degree to which it is compressed during smoothing.

Core Formula

Height per coil:

Height_per_coil = Coil_Diameter × Compression_Factor

The compression factor accounts for how much the coil flattens when pressed onto the previous layer:

• Light smoothing: 0.85 (coil retains most of its round shape)
• Moderate smoothing: 0.70 (standard technique)
• Heavy smoothing: 0.55 (coil is fully blended into the wall)

Number of coils needed:

Coils_Needed = Target_Height / Height_per_coil

Clay per coil (grams):

Each coil is essentially a cylinder. The volume of clay is: Volume = π × (Coil_Radius)² × Coil_Length

Where Coil_Length is the circumference of the vessel at that layer: Coil_Length = π × Vessel_Diameter

Clay weight = Volume × Clay_Density (approximately 1.8 g/cm³ for wet stoneware)

Worked Example

Building a vessel 20 cm tall, 15 cm diameter, with 1.5 cm coils and moderate smoothing:

• Height per coil: 1.5 × 0.70 = 1.05 cm
• Coils needed: 20 / 1.05 = 19.05, round up to 20 coils
• Length per coil: π × 15 = 47.1 cm
• Volume per coil: π × (0.75)² × 47.1 = 83.3 cm³
• Weight per coil: 83.3 × 1.8 = 149.9 g
• Total clay: 20 × 149.9 = 2,998 g ≈ 3.0 kg

Shrinkage Note

Clay shrinks 10-15% during drying and firing. Add approximately 12% to your target height if you need a specific finished size. This calculator shows the wet-building dimensions.

Coil Thickness Reference