Paint Calculator

About Paint Calculator

How the Calculation Works

Step	Formula	Example (12 x 10 ft room, 8 ft tall, 1 door, 2 windows)
Perimeter	2 x (Length + Width)	2 x (12 + 10) = 44 ft
Gross wall area	Perimeter x Height	44 x 8 = 352 sq ft
Door deduction	Doors x Door area	1 x 21 = 21 sq ft
Window deduction	Windows x Window area	2 x 15 = 30 sq ft
Net paintable area	Gross - Doors - Windows	352 - 21 - 30 = 301 sq ft
Total area (with coats)	Net area x Number of coats	301 x 2 = 602 sq ft
Gallons needed	Total area / Coverage per gallon	602 / 350 = 1.72, rounded to 2 gallons

Results are always rounded up to whole gallons because paint is sold in whole cans.

Paint Coverage Rates

Coverage varies by paint type, surface texture, and colour change. These are typical rates for a single coat on smooth drywall:

Paint Type	Coverage per Gallon (sq ft)	Coverage per Litre (sq m)	Notes
Flat / matte latex	350-400	10-12	Best coverage; hides imperfections well
Eggshell latex	300-400	9-12	Slight sheen; most popular for living areas
Satin latex	300-350	9-10	Easy to clean; good for kitchens and bathrooms
Semi-gloss latex	300-350	9-10	Durable; trim, doors, and high-moisture areas
Gloss / high-gloss	250-350	8-10	Very shiny; used for accents and furniture
Primer	200-300	6-9	Thicker; required on bare surfaces and colour changes
Ceiling paint	350-400	10-12	Usually flat/matte; thicker formula to reduce drips

How Many Coats Do You Need?

Scenario	Coats Needed	Why
Same colour touch-up	1	Matching existing colour requires minimal coverage
Similar colour change (light to light)	2	Standard for even coverage and colour depth
Dramatic colour change (dark to light)	2-3 (with primer)	Dark colours bleed through; primer blocks the old colour
Bare drywall or new plaster	1 primer + 2 topcoats	Bare surfaces absorb paint; primer seals and provides a base
Textured or rough surface	2-3	Texture absorbs more paint and requires extra to fill gaps

Standard Deduction Sizes

Opening	Typical Size	Area (sq ft)
Interior door	3 ft x 7 ft	21 sq ft
Double door / French door	5 ft x 7 ft	35 sq ft
Standard window	3 ft x 5 ft	15 sq ft
Large / picture window	5 ft x 4 ft	20 sq ft
Small bathroom window	2 ft x 3 ft	6 sq ft

The calculator uses standard door and window sizes by default. Adjust these in the settings if your openings are larger or smaller than typical.

Paint Quantity Reference by Room

Room	Typical Paintable Area	Gallons (2 coats, 350 sq ft/gal)
Small bedroom (10 x 10)	~280 sq ft	2 gallons
Standard bedroom (12 x 12)	~340 sq ft	2 gallons
Living room (15 x 20)	~500 sq ft	3 gallons
Kitchen (12 x 14)	~350 sq ft (less with cabinets)	2 gallons
Bathroom (8 x 10)	~250 sq ft	1-2 gallons
Hallway (4 x 20)	~350 sq ft	2 gallons

Tips for Accurate Paint Estimates

Tip	Why It Matters
Measure at floor level	Walls may not be perfectly square; floor measurements are more accessible
Measure height floor-to-ceiling	Do not include baseboards or crown moulding in the wall height
Subtract all openings	Doors, windows, and built-in shelves reduce paintable area significantly
Buy an extra quart	Useful for touch-ups later; store in a cool place with the colour name noted
Account for texture	Textured walls (knockdown, popcorn) use 15-25% more paint than smooth walls
Check the paint label	Coverage rates vary by brand - use the actual label value, not a generic estimate

To measure your room's floor area, the square footage calculator handles various room shapes. If you are also tiling part of the room, the tile calculator estimates tile counts and cost. All calculations run in your browser with no data stored.

How Much Does a Gallon of Paint Cost?

Interior latex paint in the US costs $20-$60 per gallon as of 2026, with premium self-priming brands running $35-$65 per gallon per Angi and HomeGuide pricing data. Low-end builder-grade paint sits near $20, while high-end designer lines (Farrow & Ball, Benjamin Moore Aura, Sherwin-Williams Emerald) push past $75. UK prices run roughly £20-£50 per 2.5 L tin for mainstream brands, with premium trade paints around £60-£90 per 5 L tub.

Tier	US price per gallon	UK price per 2.5 L	Typical brands
Budget / builder-grade	$20-$30	£15-£25	Glidden Essentials, Dulux Simply Refresh, Crown Easyclean
Mid-range	$30-$50	£25-£45	Behr Premium Plus, Valspar Signature, Dulux Easycare
Premium	$50-$75	£45-£70	Sherwin-Williams Duration, Benjamin Moore Regal, Dulux Trade Diamond
Designer / specialty	$75-$120	£70-£120	Farrow & Ball, Little Greene, Benjamin Moore Aura

Premium paints often justify the price through higher hide (fewer coats) and better washability. A $65 self-priming paint covering in one coat beats a $25 paint needing three coats once labour is factored in.

Worked Example: Painting a 14 x 12 Living Room

A 14 x 12 ft room with 9 ft ceilings, one door, and two standard windows calculates like this:

• Perimeter: 2 x (14 + 12) = 52 ft
• Gross wall area: 52 x 9 = 468 sq ft
• Door deduction: 1 x 21 = 21 sq ft
• Window deduction: 2 x 15 = 30 sq ft
• Net paintable area: 468 - 51 = 417 sq ft
• Two coats: 417 x 2 = 834 sq ft of coverage needed
• At 350 sq ft per gallon: 834 / 350 = 2.38 gallons, rounded up to 3 gallons

At $40 per gallon that is $120 in paint. Adding a gallon of primer ($25), two rollers, a brush, and painter's tape brings the DIY total to around $180. A professional would charge $350-$600 for labour and materials on the same room per HomeGuide and Angi averages for 2026.

VOC Limits and Low-Odour Paint

Volatile organic compounds (VOCs) are solvents that evaporate as paint dries, contributing to indoor air pollution and the "new paint smell". UK law (the Volatile Organic Compounds in Paints, Varnishes and Vehicle Refinishing Products Regulations 2012) caps interior matt wall and ceiling paint at 30 g/L and gloss trim paint at 130 g/L. In the US there is no single federal limit - California's SCAQMD Rule 1113 caps interior flat at 50 g/L and non-flat at 100 g/L, which most national brands now meet. "Low-VOC" typically means under 50 g/L; "zero-VOC" means under 5 g/L.

Label	VOC limit	What it means
Zero-VOC	Under 5 g/L	Safe for bedrooms, nurseries, occupied buildings
Low-VOC	Under 50 g/L (US) / 30 g/L (UK matt)	Mainstream option for residential interior work
Standard water-based	50-150 g/L	Most latex wall paints; ventilate for 24-48 hours
Oil-based / alkyd	250-450 g/L	Traditional gloss and enamel; ventilate heavily, fewer sold

Tinted paints always add some VOCs via the colourant, so a deep navy in a zero-VOC base can test at 10-20 g/L. Check GOV.UK and EPA Method 24 labelling for exact values on the tin.

Common Painting Mistakes That Waste Paint

• Skipping primer on bare drywall. Uncoated gypsum wicks 30-40% more paint than primed surface per PPG and Sherwin-Williams technical data. One coat of £20/$25 primer saves two coats of £45/$50 topcoat.
• Ignoring texture. Orange peel, knockdown, and popcorn ceilings use 15-25% more paint than smooth drywall. Knock the coverage rate from 350 down to 270 sq ft/gallon when estimating.
• Pouring from the can. Always decant into a liner or roller tray. Fresh paint in the main tin dries with a skin that flakes into the wall. Re-seal the lid with a mallet, not a foot.
• Cutting in after rolling. Cut corners and edges first with a 2-inch angled brush, then roll before the cut-in dries. Reverse order produces visible lap marks.
• Under-buying and topping up later. Paint batches can differ by 1-2 shades between production runs. Buy 10-15% more than you need in a single batch, especially for feature walls.
• Painting over damp walls. Walls below 10°C or above 85% humidity per GOV.UK Building Regulations Approved Document F cause pinholing and peeling. Use a cheap hygrometer or wait 48 hours after heavy rain.

How Many Gallons Fit Real Room Sizes?

These figures assume 8 ft ceilings, two coats, one door, two windows, and 350 sq ft per gallon. The calculator above handles custom sizes precisely.

Project	Paint needed (gallons)	Paint needed (litres)	Estimated paint cost (mid-range)
Single accent wall (12 ft long)	1 quart	1 L	$15 / £12
Small bedroom (10 x 11)	2	8 L	$70 / £55
Standard bedroom + ceiling (12 x 12)	3	12 L	$110 / £85
Living room (15 x 20)	3	12 L	$110 / £85
Whole-interior repaint (2,000 sq ft home)	10-12	40-48 L	$360-$600 / £280-£480
Exterior siding (2,500 sq ft wall area)	7-10	28-40 L	$300-$550 / £240-£440

For whole-home planning, pair this tool with the square footage calculator to map each room, then sum the gallons.

Sources

• Angi - How Much Does a Gallon of Paint Cost? 2026 Data
• HomeGuide - Paint Cost per Gallon 2026
• GOV.UK - VOC in Paints Regulations 2012
• ASTM D5324 - Standard Guide for Testing Water-Borne Architectural Coatings
• SCAQMD Rule 1113 - Architectural Coatings VOC Limits
• US EPA - VOCs and Indoor Air Quality