How much paint do I need?
Paint quantity is area maths, not guesswork from room names (“bedroom” sizes vary wildly).
- Measure the perimeter (or each wall) and multiply by ceiling height for gross wall area.
- Subtract openings — doors and windows you will not paint.
- Multiply by coats — two is the usual finish coat plan.
- Divide by coverage from the tin, then round up to pack sizes you can buy.
Run the same steps in the Paint Calculator when you want a faster pass; keep reading for bedroom judgement calls the tool will not make for you.
Coverage: US gallons and UK litres
| Market | Typical planning rate | Notes |
|---|---|---|
| US interior wall paint | ~350–400 sq ft per gallon per coat | Smooth, sealed walls; textured or bare drywall uses more |
| UK emulsion | ~10–14 m² per litre per coat | Dunelm cites ~12 m²/L; some brands claim ~14 m²/L |
Label rates assume ideal surfaces. First coats on new plaster or porous filler can drink 20–30% more. Dark-to-light colour changes often need a third coat or a tinted primer.
Bedroom worked example
Worked example — bedroom walls
US: Room 12 ft × 14 ft, 8 ft ceilings. Gross walls = 2×(12×8) + 2×(14×8) = 416 sq ft. Subtract one door (~20 sq ft) and one window (~15 sq ft) → 381 sq ft. Two coats → 762 sq ft of coverage demand. At 380 sq ft/gal → 2.0 gallons. Buy two gallons (or a gallon plus quarts if the shade is custom).
UK: Room 3.7 m × 4.3 m, 2.4 m height. Gross walls ≈ 2×(3.7+4.3)×2.4 = 38.4 m². Subtract door ~1.8 m² and window ~1.2 m² → 35.4 m². Two coats → 70.8 m². At 12 m²/L → 5.9 L. Buy a 5 L + 1 L, or two 2.5 L and a 1 L, matching the batch codes.
Answer: About 2 US gallons or about 6 UK litres for these bedroom walls at two coats — verify against your tin’s m²/L or sq ft/gal.
Ceilings and trim
Ceiling paint: length × width, same coat and coverage logic, separate product. A 12×14 ft ceiling is 168 sq ft; two coats at 350 sq ft/gal is about one gallon. Trim (skirtings, architraves) is better estimated by linear feet/metres and a small eggshell or satin tin — wall emulsion volume will not cover glossy woodwork well.
Colour changes and new plaster
- Similar colour refresh: two coats usually enough; some walls look fine with careful one-coat products if the label allows.
- Dark to light: budget a primer or third finish coat.
- New plasterboard / plaster: mist coat or primer first; do not trust full coverage rates on the first pass.
- Feature wall: calculate that wall alone if the colour differs — leftover main-wall paint will not match a different SKU.
Buying tins
Round up. A half-empty calculation still needs a full tin on the shelf. Keep one batch number for a whole room so touch-ups match. If you are painting adjoining rooms the same colour, total the areas before you buy — one larger order beats mismatched sheens from two shopping trips.
When the bedroom numbers are in hand, re-check with the Paint Calculator and adjust coverage to the exact product data sheet before you checkout.
Sheen and samples
Flat or matt hides bumps on bedroom walls; eggshell or satin on skirtings cleans better. Sheen does not change the area maths, but it changes which tin you buy — do not pour leftover wall matt onto gloss trim and call the job done.
Sample pots prevent expensive wrong colours; they do not replace the full-room litre or gallon count. Once the colour is chosen, recalculate with the real product’s coverage, not the sample pot’s tiny label. If two people paint, agree wet-edge strategy so the second coat does not show lap marks that tempt a wasteful third coat.
Exterior paint is a different calculator problem: porosity, primer and weather windows matter more than bedroom arithmetic. Keep this page for interiors; use exterior product data sheets when you move outside.
Frequently Asked Questions
How much paint for a 12×12 bedroom?
With 8 ft ceilings, one door and one window, wall area is often about 350 sq ft. Two coats at 350 sq ft/gal needs roughly 2 gallons. In metric, a similar 3.6×3.6 m room is a few litres shy of 6 L at ~11 m²/L for two coats — always use your tin’s rate.
How many gallons of paint do I need?
Gallons = (paintable sq ft × coats) ÷ coverage per gallon. Round up to whole cans. Two coats is standard for a durable finish.
How many litres of emulsion for a room?
Litres = (paintable m² × coats) ÷ m² per litre on the tin. UK DIY guides often plan ~12 m²/L; premium brands may claim up to ~14 m²/L on sealed walls.
Do I paint the ceiling with the same tin count?
No. Calculate ceiling area (L×W) separately. Ceiling paint is a different product and sheen in most rooms.
Get local quotes
For whole-house jobs, compare painters on the same room list.
USA: Angi / HomeAdvisor UK: CheckatradeSources
- Rodda Paint — Paint calculator guidance — Example ~375–400 sq ft per gallon; bedroom method.
- Dunelm — Beginners guide to painting a room — UK planning figure ~12 m² per litre; two coats.
- Victory Colours — Paint calculator — Example brand rate 14 m²/L; 4×3 m room ~5 L for two wall coats.
When you are ready to estimate materials or cost for your project, open the Paint Calculator and enter your measurements.