Stucco Mix Ratio Calculator
Calculate the quantities of cement, sand, lime, and water needed for your stucco project based on coat type, area, and thickness.
Scratch: 3/8" | Brown: 3/8" | Finish: 1/8"
Formulas Used
1. Gross Volume (ft³)
Vgross = Area (ft²) × Thickness (in) ÷ 12
2. Adjusted Volume (with waste)
Vadj = Vgross × (1 + Waste% ÷ 100)
3. Dry Material Volume (compaction factor)
Vdry = Vadj ÷ 0.67
Dry materials reduce ~33% in volume when mixed with water.
4. Individual Material Volumes
Vcement = (C ÷ (C+S+L)) × Vdry
Vsand = (S ÷ (C+S+L)) × Vdry
Vlime = (L ÷ (C+S+L)) × Vdry
5. Cement Bags (60 lb)
Bags = Vcement × 94 lb/ft³ ÷ 60 lb/bag
6. Water (gallons)
Water = Vcement × 94 lb/ft³ × 0.50 ÷ 8.34 lb/gal
Water-to-cement ratio = 0.50 by weight.
Assumptions & References
- Standard three-coat stucco system per ASTM C926 and Portland Cement Association guidelines.
- Scratch coat: 1:2.5:0.5 (cement:sand:lime), ~3/8" thick.
- Brown coat: 1:3:0.5 (cement:sand:lime), ~3/8" thick.
- Finish coat: 1:1.5:1 (cement:sand:lime), ~1/8" thick.
- Dry material compaction factor of 0.67 (i.e., dry volume ÷ 0.67 = wet volume) is a standard industry approximation.
- Portland cement bulk density: ~94 lb/ft³ (one standard 94 lb bag = 1 ft³).
- Sand bulk density: ~100 lb/ft³ (damp, loose masonry sand).
- Hydrated lime bulk density: ~40 lb/ft³.
- Water density: 8.34 lb/gallon; water-to-cement ratio of 0.50 by weight is typical for stucco workability.
- Waste factor accounts for spillage, over-application, and surface irregularities; 10% is typical.
- Results are estimates. Actual quantities may vary with surface texture, temperature, and mixing technique.
- Reference: ASTM C926 "Standard Specification for Application of Portland Cement-Based Plaster."