Enter the plaster area in square feet, pick the thickness and mix, and get cement bags plus sand in cubic feet and brass — using the 1.27 dry-volume method quantity surveyors apply.
How it's calculated
dry mortar = area × thickness × 1.27
Wet mortar volume is the area times thickness. Plaster mortar bulks when dry-batched, so the wet volume is multiplied by 1.27, then split by the mix ratio — 1:6 has 7 parts (1 cement + 6 sand), 1:4 has 5. Cement converts to 50 kg bags at 34.7 litres per bag.
Worked example — 100 sq ft at 12 mm, 1:6
100 sq ft ≈ 9.29 m². At 12 mm that is 0.111 m³ wet, 0.142 m³ dry: about 0.6 bags of cement and 4.3 cft of sand. The calculator's defaults show this case — change the thickness to 15 mm to see an external wall.
Practical allowances
Uneven masonry eats plaster: a wall that is out of plumb by even 10 mm adds a full extra coat's volume in patches. Sites typically add 10–15% on old or rough walls. Curing matters more than quantity — plaster cured for 7 days develops strength that no extra cement can substitute.
Frequently asked questions
How much cement is needed to plaster 100 sq ft?
For 12 mm internal plaster in 1:6 mix, roughly 0.6 bags (about 30 kg) of cement and 4 cft of sand per 100 sq ft. A richer 1:4 mix takes about 0.8 bags for the same area.
What plaster thickness should I use?
Common Indian practice: 12 mm for internal walls, 15–20 mm for external walls (often in two coats), and up to 20 mm where masonry is uneven. Ceilings usually take 6–10 mm, which this calculator doesn't cover.
1:4 or 1:6 — which mix ratio?
1:6 is the standard for internal wall plaster. 1:4 is richer and stronger, used for external faces, bathrooms and surfaces that take fixtures. Your specification or engineer's note wins over any rule of thumb.
Do I plaster both sides of a wall?
Usually yes for internal walls — and each face counts separately. A 10 ft × 10 ft wall plastered both sides is 200 sq ft of plaster area, so double the wall area when both faces are finished.
Reviewed on 15 August 2026. These are preliminary planning quantities from standard methods — actual consumption varies with workmanship, wastage and site conditions. VastuCalc does not provide structural design; sizes, grades and reinforcement must come from a qualified engineer.