Interior Paint Calculator

Q: How much paint do I need per square metre?

Most interior emulsion paints cover 10-14 m2 per litre for a single coat on a previously painted or sealed surface. On new or porous plaster, coverage drops to 6-10 m2 per litre. For a typical 12 m2/litre coverage over 30 m2 of walls in two coats: 30 x 2 / 12 = 5 litres. Always check the spreading rate printed on the tin, as products vary significantly. Matt and flat emulsions tend to have higher coverage than silk or satin finishes.

Q: How many coats of paint do I need?

New plaster or bare surfaces always require a mist coat (diluted emulsion, typically 10:1 paint to water) before any full coats. After the mist coat, two full coats of emulsion give a solid, even finish on most backgrounds. Going from a dark colour to a light colour (or vice versa) may require three coats to achieve full coverage. When redecorating in a similar colour to the existing paint, one coat is often sufficient if the existing surface is sound and clean.

Q: Should I use matt, silk or satin paint?

Matt emulsion is best for ceilings and low-traffic areas as it hides surface imperfections but is harder to wipe clean. Silk and satin finishes are more durable and washable, making them better for hallways, kitchens, bathrooms, and children's rooms. Eggshell is a mid-sheen finish popular for woodwork and furniture painting. For damp or high-humidity areas, use a paint specified as moisture-resistant or anti-mould. Always prime bare or new surfaces before applying a topcoat.

Q: How do I calculate paint for walls with doors and windows?

Calculate the total wall area (perimeter x height), then deduct the area of each door (typically 1.8 x 2.0 m = 3.6 m2) and each window (varies but commonly 1.0 x 1.2 m = 1.2 m2). A standard room with one door and two windows at 12 m2/litre coverage in two coats: a 4 x 3 m room with 2.4 m ceiling has a wall area of approximately 33.6 m2, less 6.0 m2 of openings = 27.6 m2. At 12 m2/litre x 2 coats, you need 4.6 litres - round up to 5 litres.

Q: Do I need to prime new plaster before painting?

Yes - new or bare plaster is very porous and will absorb a full coat of emulsion unevenly, leaving a patchy finish. Apply a mist coat first: dilute your emulsion approximately 10 parts paint to 1 part water and apply by brush or roller. The mist coat seals the plaster, prevents the suction pulling at the paint, and gives a better key for subsequent full coats. Allow the mist coat to dry fully (usually 2-4 hours) before applying full-strength emulsion. New plaster should ideally cure for at least 4-6 weeks before final decoration.

Q: What waste allowance should I use when ordering paint?

Unlike materials sold by quantity, paint waste is accounted for in the spreading rate rather than a separate percentage. However, always round up to the nearest tin size rather than down - running out mid-coat means a visible join in the finish. If the calculated amount is close to a tin boundary (e.g. 4.8 litres and tins come in 2.5 L and 5 L), buy the larger size. Keep any leftover paint for touch-ups - seal the lid tightly and store upside down to prevent a skin forming. Most emulsions stay usable for 2-3 years if sealed properly.

How much paint do I need for a room?

Calculate the exact number of litres of interior paint for walls and ceilings by entering your room dimensions. The calculator deducts doors and windows automatically, accounts for the number of coats, and applies the paint's spreading rate - so you know precisely how many tins to buy without over-ordering.

Litres and tins for walls, ceilings, woodwork, doors, and windows - primer through topcoat

Wall Paint (Emulsion)

Wall Paint Finish

Wall Coats

Coverage (m²/L) Matt: ~12 m²/L ◆ Silk: ~11 m²/L ◆ Masonry: ~5 m²/L

Ceiling Paint

Ceiling Paint Finish

Ceiling Coats

Coverage (m²/L)

Woodwork Paint (Gloss / Satin / Satinwood)

Woodwork Finish

Topcoat Coats

Coverage (m²/L) Gloss / satin typically 14-16 m²/L

Include undercoat 1 coat of undercoat on bare or repainted woodwork

Undercoat Coverage (m²/L)

Primer

Include primer coat on walls / ceiling New plaster, bare plaster, or very absorbent surfaces

Primer Coverage (m²/L)

Preferred Tin Sizes

Tick the sizes available in your chosen paint. The calculator picks the best combination to minimise waste and tins.

Waste Allowance (%)

10%

Typically 10% for cut-in edges, touch-ups, and spills. Increase for complex rooms with lots of angles.

Rooms / Areas

Job Costing (optional)

Wall paint per litre

Ceiling paint per litre

Woodwork paint per litre

Undercoat per litre

Primer per litre

Labour

Rate x total area

UK Market PricesFills in the material cost fields with current UK market prices. You can review and edit each price before applying.

Results

Total Paint Area
-
m² (all surfaces)

Total Litres Needed

all paints combined

Rooms Calculated

rooms / areas

Paint Breakdown

Surface / Paint	Area	Coats	Litres Needed	Litres to Buy	Best Tin Combo

Room Breakdown

Room	Wall Area	Ceiling Area	Wood Area	Openings	Net Paint Area

🚫 Estimate waste & skip size for this project →

Doing this as a homeowner?

Who do you actually need to hire for this?

Who do I need?

Not sure what some of these terms mean?

Browse all →

Skim Coat Render Plasterboard Bonding Coat Dry Lining Stud Wall Noggin Efflorescence Damp Proof Course Rising Damp Penetrating Damp Hygroscopic Salts Dado Rail Coving Skirting Board Lime Render Pointing Repointing Cavity Wall Breathable Membrane

Frequently Asked Questions

How much paint do I need per square metre?

Most interior emulsions cover 10-14 m² per litre on previously painted surfaces; 6-10 m²/litre on new porous plaster. Always check the spreading rate on the tin. Matt and flat finishes typically cover more than silk or satin. The calculator above uses your entered spreading rate and number of coats.

How many coats of paint do I need?

New plaster needs a mist coat (10:1 paint:water) first, then two full coats for a solid finish. Dark-to-light or light-to-dark colour changes may need three coats. Redecorating in a similar colour over a sound surface often needs just one coat.

Should I use matt, silk or satin paint?

Matt: best for ceilings and low-traffic rooms - hides imperfections but harder to wipe clean. Silk/satin: more durable and washable - better for hallways, kitchens, bathrooms, children's rooms. Eggshell: mid-sheen, popular for woodwork and furniture. Use moisture-resistant or anti-mould paint in damp areas.

How do I calculate paint for walls with doors and windows?

Calculate total wall area (perimeter x height), then deduct: door approx. 3.6 m² (1.8 x 2.0 m), window approx. 1.2 m² (1.0 x 1.2 m). The calculator above handles these deductions automatically - just enter your room dimensions and number of openings.

Do I need to prime new plaster before painting?

Yes - new plaster is very porous. Apply a mist coat first (dilute emulsion 10:1 paint:water) to seal the surface. Allow to dry fully (2-4 hours) before full coats. New plaster should ideally cure for 4-6 weeks before final decoration for best results.

What waste allowance should I use when ordering paint?

Paint waste is built into the spreading rate. Always round up to the nearest tin size - never down, as running out mid-coat leaves a visible join. Keep leftover paint sealed (lid tight, stored upside down) for touch-ups. Most emulsions stay usable for 2-3 years if properly sealed.

How Rooms Are Measured

Wall area - 2 x height x (length + width). Windows and doors are deducted.
Ceiling area - length x width of the floor plan.
Woodwork - optional. Enter a total m² estimate, or use the preset guide below.
For skirting boards, estimate 0.1 m² per linear metre of skirting. For a standard door, add ~1.8 m² per face.
Dormer windows and angled ceilings will increase wall area - add 10-15% for complex rooms.

Typical Coverage Rates

Paint type	m²/L
Matt emulsion	10-14
Silk / vinyl emulsion	10-12
Eggshell (walls)	11-13
Flat / ceiling white	12-14
Gloss / satin (wood)	13-16
Undercoat	12-14
Primer / stabiliser	7-10
Masonry paint (smooth)	5-8

Coverage varies by porosity and surface texture. New plaster and bare surfaces always absorb more - allow 15-20% extra or add a primer coat.

Woodwork Area Guide

Item	Approx m²
Standard door (both faces)	3.6
Standard door (one face)	1.8
Skirting board (per LM)	0.1
Architrave (per LM)	0.05
Window (standard casement)	0.5-1.0
Stair spindle	0.05

Reviews

★★★★★

Did you find this calculator useful? We would love to hear what you think - your feedback helps us improve.

Trade Terms

Not sure what a term means? Our plain-English glossary covers 200+ building and trade terms.

Trade Terms Dictionary

🏠 Redecorating a whole house? Our renovation cost estimator covers full redecoration projects - with trade breakdown, regional pricing and DIY saving estimates. 💧 Treating damp before you redecorate? Diagnose the type of damp first - painting over untreated damp is money wasted. Find the cause and the right fix.

Interior Paint Calculator

How much paint do I need for a room?