About Paint Calculator
Calculate how much paint you need for walls, ceilings, and trim. Enter room dimensions and number of coats to get gallons needed, coverage area, and cost estimates.
How to use
- Enter the room dimensions: length, width, and ceiling height in feet or metres. For non-rectangular rooms, calculate each wall section separately. Standard ceiling heights in Canadian homes are 8 feet (older homes) or 9 feet (newer construction).
- Specify the number and approximate size of doors and windows. Standard door openings are about 21 square feet (3x7 ft) and standard windows average 12-15 square feet. The calculator subtracts these unpainted areas from the total wall area for a more accurate paint estimate.
- Select the number of coats: one coat for touch-ups or same-colour refreshes, two coats for colour changes or new drywall (recommended for most projects). Dark colours covering light walls may require a tinted primer plus two coats. Going from dark to light may need a white primer plus two top coats.
- View the total wall area, ceiling area (if included), and gallons of paint needed based on the standard coverage rate of 350-400 square feet per gallon. The calculator uses 350 sq ft/gallon as a conservative estimate that accounts for surface texture and application method.
- Check the cost estimate based on average paint prices: economy paint ($25-$40/gallon), mid-range ($40-$60/gallon), and premium ($60-$90/gallon). Premium paints typically offer better coverage (potentially requiring fewer coats), more durable finishes, and lower VOC content.
- Add 10% to the calculated amount to ensure you have enough for touch-ups, roller absorption, and any areas that need extra attention. Running out mid-wall creates visible lap marks. Keep leftover paint sealed and labelled for future touch-ups.
Frequently asked questions
How much paint do I need for a 12x12 room?
A 12x12 room with 8-foot ceilings has 384 square feet of wall area. Subtract approximately 60 square feet for a door and two windows, leaving about 324 square feet of paintable surface. One coat requires about 1 gallon. Two coats require about 2 gallons. For the ceiling: 144 square feet requires about 0.5 gallon per coat. Total for walls (2 coats) + ceiling (1 coat): approximately 2.5 gallons. Round up to 3 gallons to have enough for touch-ups. At $50/gallon for mid-range paint, budget about $150 for a standard bedroom. For rooms with complex shapes or multiple surfaces, use the
Square Footage Calculator to get precise wall area before calculating paint quantities.
How many square feet does a gallon of paint cover?
A gallon of interior latex paint typically covers 350-400 square feet on smooth, previously painted surfaces. Coverage decreases on: textured walls and ceilings (250-300 sq ft/gallon), unpainted drywall (200-300 sq ft/gallon without primer), rough wood (200-250 sq ft/gallon), and brick or stucco (150-200 sq ft/gallon). Application method also affects coverage: rollers are most efficient, followed by brushes, then sprayers (which use 20-30% more paint due to overspray). Premium paints often have better coverage per gallon due to higher pigment and solids content, potentially saving money despite the higher per-gallon price.
Do I need two coats of paint?
Two coats are recommended for: any colour change (especially light over dark or dark over light), new unpainted drywall or plaster, patched or repaired areas, and high-traffic surfaces (hallways, kitchens, bathrooms). One coat may suffice for: repainting the same colour, using a high-quality self-priming paint on a clean surface, or minor touch-ups. Skipping the second coat to save money usually results in uneven colour, visible roller marks, and poor durability — you end up repainting sooner. The second coat adds $30-$60 in paint cost but dramatically improves the final result.
How do I calculate paint for a ceiling?
Ceiling area equals room length x room width. A 14x16 room has a 224 square foot ceiling, requiring approximately 0.6 gallons per coat. Use flat or matte finish paint for ceilings to minimize the appearance of imperfections — any sheen level highlights roller marks and drywall joints overhead. Ceiling paint is typically formulated with higher viscosity (thicker) to reduce dripping during overhead application. If the ceiling has texture (popcorn, knockdown), increase your paint quantity by 25-30% as textured surfaces absorb more paint. Consider using a dedicated ceiling white rather than matching the wall colour for a classic look that makes rooms feel taller.
Should I subtract windows and doors from the calculation?
Yes, for accuracy. A standard interior door opening (3x7 feet = 21 sq ft) and a standard window (3x4 feet = 12 sq ft) combined save you about 33 square feet per room from the paint calculation. In a small room, this represents a meaningful percentage of wall area. However, if you are estimating quickly and want to ensure you have enough paint, you can skip the subtraction — the extra paint serves as your touch-up reserve. For precise estimates (especially when buying expensive specialty paints), always subtract openings.
What paint finish should I use?
Match the finish to the room and surface. Flat/matte: ceilings and low-traffic rooms (hides imperfections but marks easily). Eggshell: living rooms, dining rooms, bedrooms (slight sheen, wipeable, most popular residential finish). Satin: kitchens, bathrooms, hallways, kids' rooms (moisture-resistant, easy to clean, moderate sheen). Semi-gloss: trim, doors, cabinets, bathrooms (durable, washable, noticeable sheen). Gloss: front doors, furniture, accent details (highest durability and sheen, shows every imperfection). Higher sheen levels are more durable and washable but also highlight wall imperfections more.
Do I need primer before painting?
Primer is recommended for: new unpainted drywall or plaster (seals the porous surface), dramatic colour changes (a tinted primer reduces the number of top coats needed), surfaces with stains (water marks, smoke damage, marker — use stain-blocking primer), glossy surfaces (primer helps paint adhere to previously glossed surfaces), and wood surfaces (prevents tannin bleedthrough, especially with cedar or redwood). Many quality paints are now paint-and-primer-in-one, which work well for repainting over existing paint in similar colours. For new construction or major colour changes, a dedicated primer still produces superior results.
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