Paint Calculator
Calculate how many gallons of paint you need for a room. Enter dimensions, subtract doors and windows, choose coats, and get your estimate.
Estimates only. Always verify quantities with a professional before purchasing materials. Building projects must comply with local codes and regulations.
About Paint Calculator
This paint calculator estimates how many gallons (or litres) of paint you need for a room. Enter the room dimensions, specify doors and windows to subtract, set coverage rate and number of coats, and get an instant estimate. An optional ceiling toggle adds the ceiling area to the total.
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.
Frequently Asked Questions
How much paint do I need for a 12x12 room?
A 12x12 room with 8-foot ceilings has about 384 square feet of wall area. After subtracting a door and two windows (about 51 sq ft), you have roughly 333 paintable square feet. With two coats at 350 sq ft/gallon, you need about 2 gallons.
How many square feet does a gallon of paint cover?
One gallon of interior latex paint typically covers 350-400 square feet per coat on smooth surfaces. Textured or porous surfaces may only get 200-300 square feet per gallon. Always check the paint can for the manufacturer's specific coverage rating.
Do I need two coats of paint?
In most cases, yes. Two coats provide better coverage, more even colour, and better durability. You might get away with one coat when painting over a similar colour with high-quality paint, but two coats is the standard recommendation.
Should I subtract doors and windows from my paint calculation?
Yes. A standard door is about 21 square feet (7x3 ft) and a standard window is about 15 square feet (5x3 ft). Subtracting these gives you a more accurate paint estimate and can save you from buying too much.
How do I estimate paint for a ceiling?
Use the checkbox option to include the ceiling in your calculation. Ceiling area is simply the room length multiplied by the width. Ceiling paint often has different coverage rates, so check your paint's specifications.
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