How to use the Plaster Quantity Calculator
- 1. Enter the areaType the area in m², or the wall size with openings and faces.
- 2. Set thickness and ratio12 mm inside, 15-20 mm outside or your value; 1:4, 1:6 or custom.
- 3. Get materialsWet and dry mortar volume, cement bags and sand.
How plaster is estimated
Wet mortar volume = area × thickness. Add an allowance (commonly 20%) for filling joints and uneven surfaces, then multiply by a dry volume factor (commonly 1.27) for voids and bulking of sand. Split the dry volume by the ratio: for 1:6, cement = dry volume × 1/7.
Cement bags = cement m³ × 1440 / 50.
Worked example and tips
100 m² of 12 mm plaster in 1:6: wet = 1.2 m³, +20% = 1.44 m³, dry = 1.44 × 1.27 = 1.83 m³. Cement = 1.83 / 7 = 0.261 m³ = 376 kg = 7.5 bags. Sand = 1.57 m³ (55 cft).
- Different offices use different allowances, so match the factors to your textbook or estimate.
- Ceiling plaster is usually thinner and richer, often 6 mm in 1:3 or 1:4.
- Deduct large openings; small ones are often ignored by measurement rules.
- For brickwork plus plaster on the same wall, run the brick calculator first and then this one, and add the cement from both.
Frequently asked questions
What thickness should I use?
Commonly 12 mm on internal brick walls, 15 to 20 mm on external walls and 6 mm on ceilings. Use your specification.
Why add 20% to wet volume?
Mortar fills brick joints and hollows in the wall, so more is used than area × thickness.
Can I plaster both faces?
Choose wall size and select both faces. The area is doubled after deducting openings from each face.
Is this calculator free?
Yes. You enter your name and WhatsApp number once to see your result, and all other Uncodemy tools then open without the form. Everything is calculated in your browser.