Does this calculator include ceiling paint?

No — this covers wall paint only. Ceilings are typically calculated separately (length × width of the ceiling area) and often use a different paint type (flat ceiling paint) than walls.

How much extra should I buy as a buffer?

Rounding up to the next available tin size usually provides enough buffer for most rooms — for larger or more complex jobs, adding a small extra litre as a top-up avoids having to source an exact colour match later if you run short mid-coat.

Why does the coverage rate matter so much?

Coverage rate varies meaningfully between paint types and brands (commonly 8-14 m²/L), so using the wrong figure can throw off the estimate by 30% or more — always check the specific tin you're planning to buy rather than assuming a generic default.

Paint Quantity Calculator — Free Home & Life Admin Calculator

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The paint aisle has a dozen tin sizes and before grabbing one at random, you want a real number for how much you actually need for the room.

Paint Quantity Calculator

Home Ownership & Renovation

Room length (m)

Room width (m)

Wall height (m)

Number of coats

Coverage per litre (m²/L, default 10)

Doors/windows to exclude (count)

Wall area = 2 × (length + width) × height − (openings × 2m² each)
Litres needed = (Wall area × coats) ÷ coverage per litre

Coverage rate varies by paint type and wall texture — check the tin's stated coverage for the most accurate result.

Reference: Standard room perimeter wall-area estimation method

ℹ️ Estimate only for household planning purposes. Not financial advice — verify against actual bills, quotes and your own financial circumstances, and consult a financial adviser for significant decisions.

1 What this calculator does

Estimates how many litres of paint are needed to paint a room's walls, based on room dimensions, number of coats, and paint coverage rate — with a simple deduction for doors and windows. A quick, consumer-friendly way to avoid buying too much or too little paint for a DIY repaint.

2 Formula & professional reasoning

Wall area = 2 x (Length + Width) x Height - (Door/window openings x 2m² each)
Litres needed = (Wall area x Coats) / Coverage per litre

A room's total wall area is calculated from its perimeter (twice the sum of length and width) multiplied by wall height, which gives the total paintable surface before accounting for openings. Each door or window is approximated as roughly 2m² of non-paintable area (a reasonable average for standard-sized openings) and subtracted. Multiplying by the number of coats and dividing by the paint's coverage rate (commonly stated on the tin, typically around 10-12 m² per litre for standard interior paint) gives the litres required — buying to this figure avoids the common problem of guessing tin sizes and either running short mid-job or overbuying.

3 Worked examples

⚠️ Illustrative example only — not clinical or professional instruction.

Basic

Small bedroom, one door, one window

Given: Length 3m, width 3m, height 2.4m, 2 coats, coverage 10 m²/L, 2 openings

Working: Wall area = 2x(3+3)x2.4 - 4 = 28.8-4 = 24.8m² | Litres = 24.8x2/10 = 4.96L

Answer: 5.0 litres needed

💡 This would typically mean buying a 4L tin plus a smaller top-up, or a single larger tin with some left over — check actual tin sizes available.

Standard

Standard living room

Given: Length 4m, width 3.5m, height 2.4m, 2 coats, coverage 10 m²/L, 2 openings

Working: Wall area = 2x(4+3.5)x2.4 - 4 = 36-4 = 32m² | Litres = 32x2/10 = 6.4L

Answer: 6.4 litres needed

💡 A typical mid-sized room — most standard 4L or two smaller tins would cover this with modest leftover for touch-ups.

Advanced

Large open-plan room, higher coverage paint

Given: Length 6m, width 5m, height 2.7m, 2 coats, coverage 12 m²/L (premium paint), 3 openings

Working: Wall area = 2x(6+5)x2.7 - 6 = 59.4-6 = 53.4m² | Litres = 53.4x2/12 = 8.9L

Answer: 8.9 litres needed

💡 Premium paints with higher coverage rates can meaningfully reduce the litres needed for the same area — worth checking the specific tin's stated coverage rather than assuming a default.

4 Sanity check

Standard interior paint coverage

Most standard interior wall paints cover 10-12 m²/litre per coat on a primed, smooth surface — check the specific tin for the manufacturer's stated figure

Textured or porous surfaces (like new plaster or heavily textured walls) typically need more paint than the stated coverage rate

Two coats is standard for most jobs

Two coats is the typical recommendation for full coverage and even colour, especially over a different existing colour or new plaster

A single coat may be sufficient for a very minor colour refresh over a similar existing colour, but this risks patchy coverage

Ceiling paint is separate

This calculator estimates wall paint only — ceilings typically need their own paint calculation (ceiling area = length × width) and often a different paint type

Buying a small buffer

Rounding up to the next available tin size, or buying a small top-up tin, avoids running short mid-coat and having to source an exact colour match later

5 Common errors

Error	Cause	Consequence	Fix
Forgetting to deduct doors and windows	Calculating wall area from the full perimeter without subtracting non-paintable openings	Overestimates the paint needed, especially in rooms with multiple doors and large windows	Enter the count of doors and windows to subtract a reasonable estimate for each, or measure actual opening sizes for a more precise deduction on rooms with unusually large openings
Using a generic coverage rate instead of the specific paint's stated figure	Assuming a default 10 m²/L coverage rate for all paint types	Different paint types (economy vs premium, matte vs gloss) have genuinely different coverage rates, sometimes significantly so	Check the specific paint tin's stated coverage rate and use that figure rather than a generic default for the most accurate result
Not accounting for surface texture or absorbency	Using a smooth-surface coverage rate for a textured, porous, or previously unpainted surface	Textured or porous surfaces absorb more paint, meaning actual coverage will be lower than the stated rate on the tin	Increase the estimated litres by 10-20% for textured, porous, or first-time-painted surfaces to account for higher absorption
Painting a much darker or lighter colour than the existing wall	Assuming standard two-coat coverage when painting a significantly different colour (e.g. dark colour over light, or vice versa)	Significant colour changes often need a third coat or a tinted primer first for full, even coverage	Budget for a possible third coat (or a tinted primer coat) when making a significant colour change, rather than assuming two coats will be sufficient