Paint Calculator
Calculate exactly how much paint you need for your project
Paint ceilings too
Pro Tip
Buy 10-15% extra paint for touch-ups, waste, and future repairs. Store leftover paint properly for years of use.
What is a Paint Calculator?
A paint calculator is an essential tool that helps homeowners, contractors, and DIY enthusiasts determine exactly how much paint they need for any project. By inputting room dimensions and accounting for doors, windows, and the number of coats required, you can avoid the frustration of running short mid-project or wasting money on excess paint. According to the Paint Quality Institute, proper paint estimation can save 15-20% on project costs by eliminating waste and return trips to the store.
How to Use This Calculator
Select Paint Type
Choose your paint finish - flat, eggshell, satin, semi-gloss, or exterior paint.
Enter Room Dimensions
Input length, width, and height for each room you plan to paint.
Account for Openings
Enter the number of doors and windows to subtract from paintable area.
Set Coats & Price
Specify coats needed and price per gallon to get accurate estimates.
Formula Explanation
Wall Area Formula
This calculates the total wall surface area by adding all four walls together. The perimeter (2 × length + 2 × width) multiplied by height gives total wall square footage.
Paintable Area Formula
Subtract door area (21 sq ft each) and window area (15 sq ft each) from walls. Add ceiling area (length × width) if painting ceilings.
Gallons Needed Formula
Multiply paintable area by number of coats, then divide by paint coverage rate (typically 300-400 sq ft per gallon depending on paint type).
Paint Coverage Rates
Example Calculations
Room: 12 ft × 10 ft × 9 ft ceiling
Openings: 1 door, 2 windows
Coats: 2 coats of eggshell paint
Wall area: 2 × (12 + 10) × 9 = 396 sq ft
Minus openings: 396 - 21 - 30 = 345 sq ft
With 2 coats: 345 × 2 = 690 sq ft coverage
Gallons: 690 ÷ 350 = 2 gallons needed
Room: 20 ft × 15 ft × 10 ft ceiling
Openings: 2 doors, 4 windows
Coats: 2 coats, including ceiling
Wall area: 2 × (20 + 15) × 10 = 700 sq ft
Minus openings: 700 - 42 - 60 = 598 sq ft
Plus ceiling: 598 + 300 = 898 sq ft
With 2 coats: 898 × 2 = 1,796 sq ft
Gallons: 1,796 ÷ 350 = 6 gallons needed
Pro Tips for Paint Projects
Buy Extra Paint
Purchase 10-15% more than calculated for touch-ups, mistakes, and future repairs. Matching paint colors later is nearly impossible.
Consider Surface Texture
Rough, textured walls absorb 15-25% more paint than smooth surfaces. Adjust your estimate accordingly.
Prime First for Coverage
Using primer on new drywall or dark colors can reduce the coats of expensive topcoat paint needed.
Store Paint Properly
Keep leftover paint in airtight containers at room temperature. Label with room name and date for easy future touch-ups.
Calculate Each Room Separately
Different rooms may need different finishes - use flat for ceilings, eggshell for living areas, semi-gloss for kitchens and baths.
Account for Accent Walls
If painting accent walls a different color, calculate those areas separately to avoid buying too much of one color.
Frequently Asked Questions
QHow much does a gallon of paint cover?
A gallon of interior paint typically covers 350-400 square feet per coat on smooth surfaces. Textured walls, porous surfaces, or dark-to-light color changes may reduce coverage by 15-25%.
QHow many coats of paint do I need?
Most projects require 2 coats for even coverage and durability. You may need 3+ coats when covering dark colors with light, painting bare drywall, or using certain reds and yellows that have poor hiding properties.
QShould I paint the ceiling?
Ceilings should be painted if they show stains, discoloration, or when doing a complete room refresh. Use flat ceiling paint which hides imperfections and doesnt reflect light that highlights flaws.
QWhat paint finish should I use?
Flat/matte for ceilings and low-traffic areas, eggshell for living rooms and bedrooms, satin for hallways and family rooms, semi-gloss for kitchens, bathrooms, and trim, and gloss for doors and cabinets.
QHow do I account for windows and doors?
Standard interior doors average 21 sq ft (3 ft × 7 ft) and windows average 15 sq ft (3 ft × 5 ft). Subtract these from your wall area to avoid overbuying paint.
QHow long does leftover paint last?
Properly stored latex paint lasts 2-10 years. Keep it sealed tightly in a cool, dry place away from freezing temperatures. If the paint separates, stirs back together smoothly, and doesnt smell bad, its still usable.
Understanding Paint & Coverage
Premium paints often require fewer coats and last longer, potentially saving money long-term. Learn more at Sherwin-Williams.
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