Painting & Walls
Paint Calculator for Walls and Ceiling UK
Enter the room dimensions in metres to calculate two-coat wall and ceiling emulsion separately. The wall takeoff deducts doors and windows; the ceiling uses length × width and keeps its own coverage, tin size, and optional price.
Formula tested · Local units · No sign-up
Project inputs
Enter measurements
Use your preferred units. Results update automatically.
Show the calculation methodFormula, conversions, rounding, and assumptions+
Wall area = 2 × (room length + room width) × wall height. A 5 m × 4 m room with 2.4 m ceilings has 2 × 9 × 2.4 = 43.2 m² of wall. You can also enter a measured wall area directly.
Standard openings are deducted: 1.9 m² per door and 1.4 m² per window (editable typical values). The remaining paintable area is multiplied by the number of coats.
Ceiling area = room length × room width. Its coats, coverage and tin size are independent of the wall-paint settings; direct-area mode asks for a separate ceiling area.
Litres = coat-area ÷ coverage per litre. Wall and ceiling tin counts are rounded up separately so a partial amount of one finish is not counted as usable stock for the other.
Real-world example
Worked example: 5 m × 4 m living room, 2.4 m ceilings, 2 coats
- Wall area: 2 × (5 + 4) × 2.4 = 43.2 m².
- Deduct openings: 1 door (1.9 m²) + 1 window (1.4 m²) = 3.3 m² → 39.9 m² paintable.
- Two coats: 39.9 × 2 = 79.8 m² to cover.
- Wall paint: 79.8 ÷ 11 m²/L = 7.25 litres → 3 × 2.5 L tins.
- Ceiling: 5 × 4 = 20 m²; two coats = 40 m²; 40 ÷ 11 = 3.64 litres → 2 × 2.5 L ceiling-paint tins.
Buy 3 × 2.5 L wall-paint tins and 2 × 2.5 L ceiling-paint tins. Enter the actual price of each product and only add VAT if the prices you enter exclude it.
Before you start
How to measure
- Measure the room's length and width in metres at skirting level, and the wall height from floor to ceiling (standard UK ceilings are around 2.4 m).
- Count doors and windows — the calculator deducts standard areas (1.9 m² per door, 1.4 m² per window). Measure bay windows and patio doors separately.
- Keep the ceiling as a separate line even if its coverage looks similar; flat ceiling paint and wall emulsion may come in different tin sizes.
- Skirting boards, architraves and other woodwork take gloss or satinwood, not emulsion — calculate them separately.
Local guidance
Notes for United Kingdom
- UK wall and ceiling paint is sold as emulsion in litres; common tin sizes are 1 L, 2.5 L, 5 L and 10 L. The 2.5 L tin is the standard retail size.
- Coverage on UK tins is quoted in m² per litre — typically 10–12 for standard emulsion on previously painted plaster; bare or fresh plaster needs a mist coat and absorbs more.
- VAT at the standard 20% rate applies to retail paint and is normally included in shelf prices; trade-counter prices are often quoted ex-VAT.
Quick reference
Typical coverage by surface (planning values — check your tin)
| Surface | Typical coverage per coat |
|---|---|
| Previously painted plaster | 10–12 m²/L |
| Fresh plaster (after mist coat) | 9–11 m²/L |
| Lining paper / woodchip | 8–10 m²/L |
| Bare masonry | 6–8 m²/L |
Editable planning values only — the coverage figure on your tin governs.
Good to know
Common mistakes to avoid
- Painting fresh plaster without a watered-down mist coat first — full-strength emulsion won't bond and coverage figures go out the window.
- Using emulsion coverage figures for skirting and doors, which take gloss or satinwood with different coverage.
- Assuming one coat will cover a strong colour change — budget for two, or more over deep reds and blues.
- Comparing a trade ex-VAT price against a retail VAT-inclusive one.
Need help?
Frequently asked questions
How much emulsion do I need for a 3 m × 3 m box room?
Wall area is 2 × 6 × 2.4 = 28.8 m². Deduct one door (1.9 m²) → 26.9 m²; two coats is 53.8 m²; at 11 m²/L that's 4.9 litres, so two 2.5 L tins covers it exactly (5 L).
How many square metres does a 5 L tin of emulsion cover?
At a typical 10–12 m² per litre, a 5 L tin covers roughly 50–60 m² in one coat — or 25–30 m² of wall at two coats. Check your tin: coverage varies by brand and finish.
Do I paint skirting boards with the same paint?
No — skirting, architrave and doors take a wood paint (gloss, satinwood or eggshell), which covers differently and is sold in smaller tins. This calculator is for the walls and ceiling emulsion.
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About this calculator
- Written by:
- BuildMeasure Editorial Team
- Technically reviewed by:
- Pending independent technical reviewer (formula unit-tested; see methodology)
- Last reviewed:
- 2026-07-20
- Formula version:
- 1.1.0
- Region reviewed for:
- United Kingdom
- Spotted an error?
- Report a correction
Methodology
- Wall area comes either from room dimensions (perimeter × wall height, i.e. 2 × (length + width) × height) or from a directly entered area. All arithmetic runs internally in SI units (m² and litres) to avoid unit drift; regional units are converted on the way in and out.
- Standard opening deductions (door and window areas, clearly labelled next to the inputs and editable via the counts) are subtracted from the wall area, floored at zero. The paintable area is multiplied by the number of coats to get the total area to cover.
- When the ceiling is included, room mode calculates its area as length × width; direct-area mode uses the ceiling area you enter. Ceiling coats, coverage, container size, and price stay separate from the wall product so the tool never silently treats two finishes as interchangeable.
- Paint volume = coat-area ÷ the coverage rate you enter. Wall and ceiling container counts are each rounded UP to the next whole container, because separate paint products cannot share a partly used can in the estimate.
- The cost estimate multiplies each container count by the matching price you enter, then applies the tax rate only when every included product has a price. No prices are built in.
- The formula is covered by automated unit tests, including hand-calculated worked examples, and is versioned (see formula version on this page).
Sources & standards
- Unit definitions: Metric units used throughout; 1 L covers coverage-rate m² per coat as stated on the tin.
- Coverage defaults: 10–12 m² per litre per coat is the typical emulsion label range; the figure on your tin governs.
This tool provides a wall-and-ceiling paint material estimate for planning purposes only. It is not a quotation, and it does not assess surface condition, primer requirements, trim paint or colour-change coverage. Confirm quantities and each product's coverage rate with your paint supplier before buying.