Cob Building Calculator

Clay, sand, and straw volumes for cob construction.

Total wall length (ft)

Wall height (ft)

Wall thickness (in)

Tab to move between fields

Wall volume (cu ft)

240

Clay soil (cu yd)2.22

Sand/gravel (cu yd)5.33

Straw bales12

How to Use This Calculator

Enter Total Wall Length and Wall Height in feet, and Wall Thickness in inches.
Review Wall Volume (cu ft) to understand the scale of the cob project.
Check Clay Soil (cu yd), Sand/Gravel (cu yd), and Straw Bales needed for the cob mix.
Use these quantities to source materials and plan mixing sessions.
Factor in drying time between lifts — typically 1-3 inches per day in dry climates.

How the result changes with Total wall length (ft)

Identify Input Parameters
Total wall length (ft) = 20, Wall height (ft) = 8, Wall thickness (in) = 18 = 3 input(s) provided
Calculate Wall volume
Wall volume = wallLength * wallHeight * (wallThickness / 12)
240 = 240
Calculate Clay soil
Clay soil = round((wallVolCuFt * 0.25) / 27 * 100) / 100
2.22 = 2.22
Calculate Sand/gravel
Sand/gravel = round((wallVolCuFt * 0.60) / 27 * 100) / 100
5.33 = 5.33