Plaster Calculator
Plaster material equals the net wall area multiplied by the thickness, then by the dry factor of 1.54, split by the mix ratio. A 200 sq ft wall at 12 mm in 1:4 mix needs roughly 3 cement bags and 10 cu ft of sand.
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Formula
- Net area = Wall area - openings
- Wet volume = Net area x thickness in feet
- Dry volume = Wet volume x 1.54
- Cement = Dry volume x 1/(1+n), divided by 1.25 cu ft per bag
- Sand = Dry volume x n/(1+n)
Worked Example
| Input | Value |
|---|---|
| Wall | 20 x 10 ft = 200 sq ft |
| Thickness | 12 mm (0.5 in) |
| Mix | 1:4 |
| Dry volume | 12.83 cu ft |
| Cement | 3 bags |
| Sand | 10.27 cu ft |
Frequently Asked Questions
What thickness should plaster be?
Internal walls are usually 12 mm, external walls 15 to 20 mm, and ceilings 6 to 12 mm.
Which plaster mix ratio should I use?
1:4 suits most internal work, 1:6 is economical for internal walls, and 1:3 to 1:4 is used externally for weather resistance.
Do I deduct doors and windows from plaster area?
Yes. Deduct full openings above about 5 sq ft. Very small openings are usually ignored as the reveal compensates.
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Estimates only. Quantities follow recognised standards (ACI 318, CRSI, IRC 2021, IS-1077, PBQS); actual site consumption varies with workmanship, wastage and detailing. Confirm with a licensed engineer before ordering.