Openings / excluded areas
Doors, windows or other rectangular deductions for Room 1.
Net paintable area: 41.67 m²
Room and project paint estimator
Paint Calculator
Estimate multiple rooms or wall groups with opening deductions, coats, manufacturer coverage, waste, purchase rounding and cost.
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Rooms and surfaces
Add a single wall, a complete room, or several separate paint areas. Openings are deducted per item.
Coats, coverage and purchasing
Coverage must come from the selected product. Purchase rounding can represent the pack size you plan to buy.
Coverage varies with substrate porosity, texture, colour change, primer, application method and product specification. Use the manufacturer figure for the exact paint and surface.
Wall Area, Coat Area and Paint Volume
Wall area is the physical surface after openings are deducted. Coat-area multiplies that surface by the number of coats. Paint volume divides coat-area by the selected product coverage, then applies waste and purchase-pack rounding.
Worked Example: One Room
A 5 m × 4 m room at 2.5 m high has 45.0 m² of gross wall area. Deducting a 0.9 × 2.1 m door and 1.2 × 1.2 m window leaves 41.67 m². Two coats at 10 m²/L require 8.33 L before allowance.
Worked Example: Repeated Corridor Walls
Two 12 m × 2.7 m walls provide 64.8 m² gross area. With 6 m² of openings, three coats create 176.4 m² of coat-area; at 9 m²/L this is 19.6 L before waste and pack rounding.
Product and Surface Conditions Matter
New plaster, masonry, rough render and strong colour changes can consume more paint than a smooth sealed surface. Primer, spray losses and touch-up stock should be handled as explicit assumptions rather than a hidden universal allowance.
Paint Calculator FAQ
Why can manufacturer coverage differ from calculated coverage?
Published coverage is usually measured under defined conditions. Porous or textured substrates, application method, thinning, overspray and film-build requirements can reduce the area achieved by one litre or gallon.
How do multiple coats affect litres required?
The calculator multiplies net paintable area by the number of coats before dividing by product coverage. Two coats therefore double coat-area, although primer and finish coats with different coverage should be estimated separately.
Should doors and windows be deducted?
Deduct significant unpainted openings. Small openings are sometimes left in a preliminary estimate to offset cutting-in losses, but the transparent opening list lets you choose the approach deliberately.
Can I estimate several rooms at once?
Yes. Add full rooms, single walls or repeated wall groups. Each item can have its own doors, windows and other rectangular deductions.
What coverage value should I use?
Use the product label or technical data sheet for the actual coating and substrate. Estimate primer, undercoat and finish products separately when their coverage differs.