Wall Plaster Calculator

How it works

wet volume = area × thickness · dry volume = wet volume × (1 + extra) × 1.27 · cement = dry volume ÷ (1 + n) × 1,440 kg/m³ · sand = dry volume × n ÷ (1 + n) (mix 1 : n)

Plaster (render, repello, enlucido) is a cement–sand mortar spread 6–25 mm thick. The wet volume is the wall area times the thickness; an allowance (usually 20%) covers hollows, joints and spillage, and the 1.27 factor converts the wet mortar into the larger volume of loose dry cement and sand needed, because the mixing water and the cement paste fill the voids between sand grains. The dry volume is then split by the mix ratio and the cement is converted to bags with its bulk density of 1,440 kg/m³. Richer mixes (1:3, 1:4) are used outside and in wet areas; leaner 1:5–1:6 mixes inside.

Worked example

A 50 m² wall plastered 12 mm thick in 1:4 with a 20% allowance: wet volume = 50 × 0.012 = 0.6 m³; dry volume = 0.6 × 1.2 × 1.27 = 0.914 m³. Cement = 0.914 ÷ 5 × 1,440 = 263 kg → 5.3, so buy 6 bags of 50 kg; sand = 0.914 × 4 ÷ 5 = 0.73 m³ (about 1,170 kg). That is 5.27 kg of cement per m².

Sources: IS 1661:1972 Code of practice for cement and cement-lime plaster finishes (Bureau of Indian Standards) · Portland Cement Association — Plaster/Stucco

Frequently asked questions