Paint Calculator
Paint quantity is the net area divided by the coverage rate, multiplied by the number of coats. Emulsion covers about 325 sq ft per gallon. A 15 x 12 ft room with a 10 ft ceiling needs roughly 4.1 gallons (15.5 litres) for primer plus two coats.
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Formula
- Wall area = 2 x (Length + Width) x Height
- Net wall = Wall area - doors (21 sq ft each) - windows (16 sq ft each)
- Total area = Net wall + ceiling (Length x Width) if painting the ceiling
- Primer = Total area / 375 x 1.10
- Finish = Total area x coats / coverage rate x 1.10
- Litres = Gallons x 3.785
Worked Example
| Input | Value |
|---|---|
| Room | 15 x 12 ft, 10 ft ceiling |
| Wall area | 540 sq ft |
| Openings | 1 door + 1 window = 37 sq ft |
| Ceiling | 180 sq ft |
| Total area | 683 sq ft |
| Primer | 2.01 gal |
| Finish, 2 coats emulsion | 4.63 gal |
| Total | 6.64 gal = 25.1 litres |
Frequently Asked Questions
How many square feet does a gallon of paint cover?
Emulsion covers about 325 sq ft, primer 375 sq ft, oil-based 275 sq ft and textured paint 150 sq ft per gallon.
How many coats of paint do I need?
Two coats over primer is standard. Use three when covering a dark colour with a light one.
How many litres is a gallon of paint?
One US gallon is 3.785 litres.
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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.