Plaster quantity calculator
Work out how much cement and sand a plastering job needs — from the area (or length × height), the coat thickness and the mortar ratio, using the standard dry-mortar factor of 1.27.
Built for Nepali site practice with 1:4 and 1:6 cement-sand mixes, a 12 mm default coat, and results in cement bags plus sand in both cubic feet and cubic metres. A planning-level tool, computed in your browser.
Plaster details
Total surface to be plastered (deduct large openings).
Internal walls ≈ 12 mm; external / ceilings ≈ 15–20 mm.
1:4 is a rich mix for external / wet areas; 1:6 is common for internal walls.
Cement required
8.8 bags
439 kg of cement (50 kg bags)
Sand
43.1 cft
Plaster area
100.0 m²
Sand volume
1.219 m³
Dry mortar
1.524 m³
Cement bags
8.8
| Mortar ratio | 1 : 4 (5 parts total) |
| Wet plaster volume | 100.0 m² × 12 mm = 1.200 m³ |
| Dry mortar (×1.27) | 1.200 m³ × 1.27 = 1.524 m³ |
| Cement volume | 1.524 × 1/5 = 0.305 m³ |
| Cement bags | 0.305 m³ × 1440 ÷ 50 = 8.8 bags |
| Sand quantity | 1.219 m³ = 43.1 cft |
A planning-level estimate using the standard dry-mortar factor of 1.27 (mortar shrinks roughly 27% when batched dry) and a cement bulk density of 1440 kg/m³ per 50 kg bag. Add 10–20% for wastage, uneven surfaces and the dado / chamfer coat. Actual yield varies with sand bulking, surface roughness and workmanship — verify against your supplier's mix and site conditions.
From wall area to cement bags
The volume of finished plaster comes from area and thickness; the dry materials take up more space, then split by the mortar ratio into cement and sand.
Wet & dry volume
Wet plaster = area × thickness. Multiply by 1.27 because dry cement and sand occupy ~27% more volume than the finished coat.
Split by ratio
Divide the dry mortar by the cement:sand parts — for 1:4 that is 1 part cement and 4 parts sand out of 5.
Bags & cubic feet
Cement volume × 1440 kg/m³ ÷ 50 gives bags; sand volume × 35.3147 converts cubic metres to cubic feet for ordering.
Plastering, answered
How do you calculate plaster quantity?+
First find the wet plaster volume = area × thickness (e.g. 100 m² × 12 mm = 1.2 m³). Multiply by the dry-mortar factor of 1.27 to get the dry mortar volume, then split it by the cement:sand ratio. Cement bags = cement volume × 1440 kg/m³ ÷ 50, and sand is the remaining volume, converted to cubic feet (1 m³ = 35.3147 cft).
Why multiply the wet volume by 1.27?+
Wet mortar shrinks when you batch the dry ingredients because cement and sand fill the voids between particles and water is added afterwards. The dry materials therefore occupy roughly 27% more volume than the finished plaster, so a factor of about 1.27 (sometimes 1.30) is applied to convert wet plaster volume to dry mortar volume.
What plaster thickness should I use?+
Internal wall plaster is usually 12 mm, external (weather) faces and ceilings are often 15–20 mm, and rough or uneven masonry may need more. This calculator defaults to 12 mm; change it to match your specification. A thicker coat needs proportionally more cement and sand.
Should I use a 1:4 or 1:6 cement-sand ratio?+
A 1:4 mix is richer and stronger, preferred for external walls, wet areas (bathrooms, kitchens) and the first coat on rough surfaces. A 1:6 mix is economical and common for internal walls and ceilings. Always follow your structural drawings or engineer's specification.
Does this include an allowance for wastage?+
No. The result is the theoretical material quantity. In practice add about 10–20% extra for wastage, uneven surfaces, the dado/chamfer coat, sand bulking and site spillage. For ordering, round cement up to whole bags.
How many cement bags are in one cubic metre?+
Using a bulk density of 1440 kg/m³ and 50 kg bags, one cubic metre of cement is about 28.8 bags. This calculator uses those figures, which match standard Nepali and Indian practice, to convert the cement volume into bags.
Sources & data note
Based on standard plastering practice: dry mortar = wet plaster volume × 1.27, a cement bulk density of 1440 kg/m³ in 50 kg bags, and 1 m³ = 35.3147 cft. The dry-mortar factor (often quoted as 1.27–1.30) and sand bulking vary with materials. These are indicative quantities before wastage — add 10–20% and verify against your specification and supplier.