Paint Calculator
Calculate paint coverage, gallons needed, and cost for interior/exterior projects
Calculate Paint
Get exact paint quantities
Standard 20 sq ft each
Standard 15 sq ft each
2 coats recommended
Average paint: $30-$50/gallon
💡 Painting Pro Tips
- 1One gallon covers ~350 sq ft per coat. Always buy 10% extra for touch-ups
- 2Use primer on new drywall, dark colors, or when making dramatic color changes
- 3Two coats provide better coverage and durability than one thick coat
- 4Premium paint ($40-60/gal) requires fewer coats than budget paint ($20-30/gal)
- 5Allow 2-4 hours drying time between coats in normal conditions
Related Calculators
How to Use This Calculator
Using the Paint Calculator begins with accurate room measurements. Measure the length and width of each wall using a tape measure, recording measurements in feet. For ceiling height, measure from floor to ceiling—most residential rooms are 8 feet, but verify yours. Count all doors (standard size is 20 square feet each) and windows (standard 15 square feet). The calculator automatically subtracts these non-paintable areas from the total wall area, ensuring you don't overbuy paint for spaces that won't be painted.
Select your room type from the options provided: standard room, bathroom, kitchen, or bedroom. This helps the calculator apply appropriate defaults based on typical room characteristics. Bathrooms often have more fixtures and smaller wall areas, while bedrooms tend to be larger with more windows. Enter the number of paint coats you plan to apply—two coats is the professional standard for best coverage and color accuracy, though dark-to-light or light-to-dark color changes may require three coats.
Input your local paint price per gallon. Quality interior paint ranges from $25-40 per gallon for good brands like Behr or Valspar, $40-60 for premium brands like Benjamin Moore or Sherwin-Williams, and $60-80 for specialty paints. The calculator computes both paint and primer requirements. Primer is essential when painting new drywall, covering dark colors, making dramatic color changes, or painting over stains. One coat of primer followed by two coats of paint is the standard professional application.
Review your results which display gallons of paint needed (rounded up to the nearest gallon since paint is sold in whole gallons), primer requirements (typically one coat covering the entire area), total coverage area in square feet, and complete project cost including both paint and primer. The calculator includes a 10% waste factor to account for spillage, roller/brush absorption, and touch-ups. Always buy one extra gallon for future touch-ups—paint batches can vary slightly in color, and having matching paint years later is invaluable.
Understanding Paint Calculations
Paint coverage is the fundamental concept in paint calculation, measured in square feet per gallon. Professional-grade interior paint covers approximately 350-400 square feet per gallon per coat on smooth, previously painted surfaces. This coverage assumes proper application with quality rollers and techniques. Lower-quality paint may cover only 250-300 square feet per gallon, requiring more paint and potentially more coats for good coverage. Textured surfaces like popcorn ceilings, rough drywall, or brick reduce coverage by 20-30% because paint fills texture cavities.
Wall area calculation follows a simple formula: perimeter times height. For a rectangular room, calculate (length + length + width + width) × height, or 2(length + width) × height. This gives you total wall area before subtracting doors and windows. Standard interior doors measure approximately 20 square feet (3 feet wide × 6.67 feet tall), while standard windows average 15 square feet (3 feet × 5 feet). Large sliding doors, picture windows, or French doors require individual measurement and subtraction.
The two-coat standard exists for good reasons beyond achieving full color coverage. The first coat provides initial coverage and color blocking but often shows thin spots, roller marks, or uneven sheen. The second coat fills in imperfections, evens out color and sheen, and provides durability and washability. Attempting to achieve perfect coverage in one thick coat leads to runs, drips, and uneven drying. Some situations require three coats: covering very dark colors with light paint, painting over bold colors like red or orange, covering repaired drywall patches, or achieving full coverage of deep, vibrant colors.
Primer serves multiple critical functions and should never be skipped when needed. New drywall is extremely porous and will absorb multiple coats of paint, wasting paint and money—primer seals the surface. Dark-to-light color changes require primer to block the old color; otherwise, you'll need 3-4 coats of paint. Water stains, smoke damage, or marker/crayon marks bleed through regular paint—stain-blocking primer prevents this. Glossy surfaces like old oil-based paint or laminate cabinets won't hold new paint without bonding primer. Primer typically costs $20-30 per gallon, less than paint, making it economical insurance.
Paint quality dramatically affects coverage, durability, and project cost. Budget paint ($20-30/gallon) has less pigment and binder, requiring 3+ coats for full coverage, more frequent repainting, and poor washability. Mid-grade paint ($30-50/gallon) offers good coverage in 2 coats, decent durability, and moderate washability—ideal for most residential projects. Premium paint ($50-80/gallon) provides excellent one-coat coverage, superior durability, stain resistance, and washability. For high-traffic areas, hallways, or children's rooms, premium paint saves money long-term by lasting years longer and cleaning better. Bathrooms and kitchens benefit from mildew-resistant paint formulations.
Formula & Calculations
The basic paint calculation formula starts with total wall area: Wall Area = 2(Length + Width) × Height. For a 12-foot by 15-foot room with 8-foot ceilings: 2(12 + 15) × 8 = 2(27) × 8 = 432 square feet of wall area. This represents the gross wall surface before any subtractions. For ceilings, use Length × Width: 12 × 15 = 180 square feet. Always measure each wall individually in irregularly shaped rooms and sum the areas.
Subtract doors and windows from gross wall area. Standard interior door = 20 square feet, standard window = 15 square feet. For our example with 2 doors and 3 windows: 432 - (2 × 20) - (3 × 15) = 432 - 40 - 45 = 347 square feet of paintable wall area. Large or non-standard openings should be measured individually. Sliding doors (6-8 feet wide) range from 50-80 square feet. Picture windows can be 30-50 square feet. French doors with glass panels still subtract approximately 18 square feet.
Calculate gallons needed using the coverage rate and number of coats. Paint coverage = 350 square feet per gallon (standard for quality paint). Gallons = (Paintable Area × Number of Coats) ÷ Coverage Rate. For our example with 2 coats: (347 × 2) ÷ 350 = 694 ÷ 350 = 1.98 gallons. Always round UP—you cannot buy partial gallons, so purchase 2 gallons. For ceiling paint (if painting ceiling): 180 ÷ 350 = 0.51 gallons, round up to 1 gallon.
Primer calculation typically uses the same paintable area but requires only one coat. Primer coverage is similar to paint (350-400 sq ft/gallon). For our example: 347 ÷ 350 = 0.99 gallons, round to 1 gallon. If painting the ceiling, add ceiling area: (347 + 180) ÷ 350 = 1.5 gallons, round to 2 gallons primer. Total project cost = (2 gallons paint × $45) + (1 gallon primer × $25) = $90 + $25 = $115 for walls, or $205 if including ceiling. Add 10-15% ($12-32) for supplies: rollers, brushes, painter tape, drop cloths, paint trays.
Key Factors to Consider
Surface condition dramatically impacts paint requirements and project success. New drywall requires primer plus two coats of paint—attempting to skip primer wastes paint as drywall absorbs the first 2-3 coats. Repaired drywall with spackling or joint compound must be primed or the patched areas will show through as dull spots. Previously painted smooth walls in good condition offer the easiest painting with best coverage. Textured walls (orange peel, knockdown, popcorn) require 20-30% more paint due to increased surface area. Glossy surfaces like old oil-based paint need deglosser or bonding primer—new paint won't adhere properly to slick surfaces.
Color changes affect both primer and paint requirements significantly. Light to light (beige to white) or dark to dark (navy to black) typically needs only two coats of paint with no primer if the existing paint is in good condition. Light to dark (white to navy) requires two coats for full coverage and deep color saturation. Dark to light (burgundy to cream) absolutely requires stain-blocking primer plus 2-3 coats of paint—attempting this without primer means 4-5 coats of expensive paint. Bright or bold colors (red, orange, yellow, deep purple) may require tinted primer for best coverage.
Ceiling height impacts material costs more than homeowners expect. Standard 8-foot ceilings are the baseline for all calculations. Nine-foot ceilings increase wall area by 12.5%, and 10-foot ceilings increase by 25%—substantially impacting paint requirements. Vaulted or cathedral ceilings require careful area calculation accounting for sloped surfaces. Two-story foyers or great rooms with 16-20 foot walls need scaffolding rental ($100-200) and may require professional help for safety. Extremely high ceilings may benefit from professional paint spraying rather than rolling.
Paint quality affects both coverage and long-term costs. Budget paint ($20-30/gallon) contains less pigment and more fillers, offering 250-300 sq ft coverage and requiring 3+ coats. Mid-grade paint ($35-50/gallon) provides 325-375 sq ft coverage and achieves full coverage in 2 coats. Premium paint ($50-80/gallon) delivers 375-400 sq ft coverage, often achieving excellent coverage in 1-2 coats. For a 2,000 sq ft painting project (5-6 rooms), budget paint might need 16 gallons ($400) with questionable durability, while premium paint needs 12 gallons ($720) but lasts twice as long and cleans better—better long-term value.
Room function determines appropriate paint finish and specialty requirements. Flat/matte paint (lowest sheen) hides imperfections best but shows marks and doesn't clean well—use only in low-traffic areas like ceilings and adult bedrooms. Eggshell (slight sheen) offers better cleanability for living rooms and dining rooms. Satin (subtle shine) works well in hallways, children's rooms, and family rooms—wipes clean easily. Semi-gloss (noticeable shine) is ideal for kitchens, bathrooms, and trim—highly washable and moisture-resistant. Gloss (high shine) suits only cabinets, doors, and trim requiring frequent cleaning. Kitchens and bathrooms benefit from mildew-resistant formulations adding $5-10 per gallon.
Frequently Asked Questions
1How much paint do I need for a 12x12 room?
A 12x12 room with 8-foot ceilings requires approximately 2-3 gallons of paint for walls (2 coats) and 1 gallon for the ceiling. Wall calculation: 2(12+12) × 8 = 384 sq ft minus doors/windows (typically 50 sq ft) = 334 sq ft × 2 coats = 668 sq ft ÷ 350 coverage = 1.9 gallons, round to 2. Ceiling: 12 × 12 = 144 sq ft ÷ 350 = 0.4 gallons, round to 1. Total 2-3 gallons for walls plus 1 for ceiling. Add 1 gallon primer if painting new drywall or making major color changes. Total cost: approximately $150-200 including paint, primer, and supplies.
2Is one gallon of paint enough for one room?
One gallon of paint is rarely enough for an entire room. One gallon covers approximately 350-400 sq ft per coat. Small bathrooms or powder rooms (5×8 feet, 208 sq ft of walls) might fit in one gallon for two coats, but most rooms require 2-4 gallons. A typical 10×12 bedroom has ~350 sq ft of paintable wall area needing 2 gallons for two coats. Living rooms typically need 3-4 gallons. Always calculate your specific room and round up—leftover paint is useful for future touch-ups, while running short mid-project means buying another gallon and potentially dealing with batch color variation.
3How many square feet does a gallon of paint cover?
One gallon of quality paint covers approximately 350-400 square feet per coat on smooth, previously painted surfaces. Coverage varies by paint quality: budget paint covers 250-300 sq ft, mid-grade covers 325-375 sq ft, and premium paint covers 375-400 sq ft. Surface texture significantly affects coverage—textured or rough surfaces may reduce coverage by 20-30%. New drywall or porous surfaces absorb more paint, reducing coverage to 200-300 sq ft. Always check the specific coverage rate on your paint can and add 10% for waste, touch-ups, and variations in application technique.
4Do I need primer before painting?
Primer is essential in several situations: (1) New drywall—absolutely requires primer or you'll waste 2-3 coats of expensive paint on absorption, (2) Dark to light color changes—without primer you'll need 3-4+ coats for coverage, (3) Stain coverage—water stains, smoke damage, or marker will bleed through paint without stain-blocking primer, (4) Glossy surfaces—old oil-based paint or laminate won't hold new paint without bonding primer, (5) Bare wood—requires primer for even stain and finish. You can skip primer only when repainting similar colors over existing paint in good condition. Primer ($20-30/gallon) saves money by reducing paint coats needed.
5How long does paint last after opening?
Properly stored paint lasts 2-5 years after opening. Store opened paint cans in climate-controlled environments (50-80°F)—freezing ruins paint, and extreme heat reduces shelf life. Tap the lid on firmly with a rubber mallet, creating an airtight seal. Store cans upside down for the first 24 hours to create a paint seal on the lid, then store right-side up. Latex paint develops skin or mold growth when old—skim off and test on cardboard before using. Oil-based paint can last 10-15 years if sealed properly. Label cans with room name and date painted. Dried-out paint cannot be revived—dispose properly at household hazardous waste facilities.
6How many coats of paint should I apply?
Two coats of paint is the professional standard for all interior painting projects. The first coat provides base coverage and color blocking but typically shows thin spots, roller marks, or sheen inconsistencies. The second coat evens out coverage, eliminates imperfections, and provides durability. Some situations require three coats: covering very dark colors (red, navy, black) with light paint, painting vibrant colors over white, covering repaired drywall, or painting new drywall without primer. One-coat paint claims are marketing—even premium one-coat paints achieve better results with two coats. High-traffic areas benefit from a third coat for added durability and washability.
7Should I paint walls or ceiling first?
Always paint the ceiling first, then walls, then trim—this order minimizes touch-ups and creates the cleanest finish. Ceiling painting inevitably splatters on walls (even with careful technique), so painting the ceiling first means these splatters get covered when you paint walls. Cut in ceiling edges first (where ceiling meets walls), then roll the ceiling. After ceiling dries (4-6 hours), tape off the ceiling-wall junction and paint walls. Finally, paint trim and baseboards last—they're easiest to tape off and any wall paint splatter on trim gets covered. Use painter's tape designed for delicate surfaces when taping newly painted areas. Remove tape while paint is still slightly damp (not fully dried) for cleanest lines.