This plaster calculator works out the cement and sand you need to plaster a wall. Enter the wall area, plaster thickness, and mix ratio above to get bags of cement and the volume of sand required.
How to use this calculator
- Enter the wall area in square feet.
- Enter the plaster thickness and the ratio (e.g. 1:4).
- Read the cement bags and sand needed.
How is plaster quantity calculated?
Wet volume = Area × (Thickness ÷ 12) Dry volume = Wet volume × 1.27 Cement = Dry volume × (1 ÷ ratio parts) Sand = Dry volume × (sand part ÷ ratio parts)
Example calculation
For 100 ft² at 0.5 inch thick, ratio 1:4:
- Wet volume = 100 × (0.5 ÷ 12) = 4.17 ft³
- Dry volume = 4.17 × 1.27 = 5.29 ft³
- Cement = 5.29 ÷ 5 = 1.06 ft³ → about 1 bag (94 lb)
- Sand = 4.2 ft³
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Frequently Asked Questions
How do I calculate plaster quantity?
Multiply the wall area by the plaster thickness for wet volume, multiply by about 1.27 for dry volume, then split by your cement-to-sand ratio.
What is the best mix ratio for plastering?
A 1:4 cement-to-sand ratio suits internal walls, while 1:6 is common for lighter coats. Richer 1:3 is used for external and wet areas.
What thickness should wall plaster be?
Internal plaster is usually 0.5 inch (12 mm) thick; rough external walls may need 0.6–0.75 inch to level the surface.