Trade & Construction
Estimate wall paint litres, cans and material cost from room length, width, height, openings, coats, coverage rate and waste allowance, with a printable job note.
Calculator
Wall area = 2 × (room length + room width) × wall height. Net paint area = max(0, wall area − openings). Coated area = net paint area × coats. Paint litres = coated area ÷ coverage per litre. Order litres = paint litres × (1 + waste percent ÷ 100). Cans = ceiling(order litres ÷ can size).
This is the method behind the answer, so the result can be checked rather than simply trusted.Visual grid
Length, area, volume and material estimates are grid problems too: measure the space, account for edges and allowances, then turn the pattern into a number you can use.
Space calculations turn a real surface, room, run or volume into cells, edges and allowances that can be quoted, ordered or checked.
CalculationTime
Wall area = 2 × (room length + room width) × wall height. Net paint area = max(0, wall area − openings). Coated area = net paint area × coats. Paint litres = coated area ÷ coverage per litre. Order litres = paint litres × (1 + waste percent ÷ 100). Cans = ceiling(order litres ÷ can size).
Use this space on the printed report for client, supplier, classroom, job-location, measurement, quote or approval notes.
Wall area = 2 × (room length + room width) × wall height. Net paint area = max(0, wall area − openings). Coated area = net paint area × coats. Paint litres = coated area ÷ coverage per litre. Order litres = paint litres × (1 + waste percent ÷ 100). Cans = ceiling(order litres ÷ can size).
For a 5 m by 4 m room with 2.4 m walls, gross wall area = 2 × (5 + 4) × 2.4 = 43.2 m². Subtract 4 m² of openings to get 39.2 m². Two coats cover 78.4 m². At 10 m²/L, base paint is 7.84 L. With 10% allowance, order about 8.62 L, or 3 cans if cans are 4 L each.
Master’s Tip: do not hide the coverage rate. Paint labels often give a best-case range, and porous plaster, strong colour changes, textured walls or spray application can move the real litres. Print the rate and waste allowance beside the result before buying.
Standard or basis: transparent rectangular wall-area arithmetic using metric dimensions, user-entered paint coverage in m²/L per coat, upward can rounding and a separate waste/touch-up allowance. Manufacturer instructions and local safety guidance override generic estimates.
Methodology & Accuracy
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Wall area = 2 × (room length + room width) × wall height. Net paint area = max(0, wall area − openings). Coated area = net paint area × coats. Paint litres = coated area ÷ coverage per litre. Order litres = paint litres × (1 + waste percent ÷ 100). Cans = ceiling(order litres ÷ can size).
Standard or basis: transparent rectangular wall-area arithmetic using metric dimensions, user-entered paint coverage in m²/L per coat, upward can rounding and a separate waste/touch-up allowance. Manufacturer instructions and local safety guidance override generic estimates.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master’s Tip: do not hide the coverage rate. Paint labels often give a best-case range, and porous plaster, strong colour changes, textured walls or spray application can move the real litres. Print the rate and waste allowance beside the result before buying.
Calculate wall area, subtract large openings, multiply by the number of coats, divide by the paint coverage rate, then add a waste or touch-up allowance.
It depends on room size, wall height, openings, coats and coverage. A 5 m by 4 m room with 2.4 m walls, 4 m² of openings, two coats and 10 m²/L coverage needs about 8.62 L with a 10% allowance.
Subtract large doors, windows or skipped sections when they materially reduce painted area. Small openings may not reduce the number of cans because cutting-in and touch-ups still use paint.
Use the coverage rate from the paint tin or manufacturer data sheet when possible. If you do not know it, 10 m² per litre per coat is a common planning value, but real coverage varies by product and surface.
Print room dimensions, openings, coats, coverage rate, waste allowance, litres, rounded cans, optional price, formula and notes about surface condition or colour change.
Paint estimating turns room geometry into liquid quantity, but the real-world variable is coverage. A useful paint record keeps surface area, coats, manufacturer coverage, waste and can rounding separate instead of hiding them inside one unexplained number.
Paint is usually specified by coverage: how many square metres one litre covers for one coat. That means the room must first be reduced to a net wall area before litres can be estimated.
Two coats do not change the room size, but they double the coated area. Primer, undercoat or stain blocking should be planned separately when the product system requires it.
Smooth sealed walls can use less paint than porous plaster, masonry or textured surfaces. The calculator therefore makes coverage editable and prints it beside the answer.
Paint is purchased in tin sizes, not exact decimal litres. Rounding litres up to cans keeps the shopping list practical while preserving the calculated litres for checking.