Paint Calculator
Calculate how many gallons of paint you need for your room. Includes coverage for doors, windows, and multiple coats.
Room Dimensions
Units:
Paint Type:
Paint Needed
2 gallons
(7 liters)
Area Breakdown:
Tip: Always buy a little extra paint (10-15% more) for touch-ups and to account for variations in wall texture and absorption.
Paint Coverage Guide
Interior Paint
350-400 sq ft per gallon
Smooth walls, 2 coats recommended
Exterior Paint
250-400 sq ft per gallon
Varies by surface texture
Primer
200-300 sq ft per gallon
Porous surfaces need more
When to Use Primer
- • New drywall or plaster
- • Painting over dark colors
- • Stained or patched areas
- • Changing from oil-based to latex paint
- • Painting wood or metal for the first time
What Is Paint Calculation?
Paint calculation determines how much paint you need based on surface area, coverage rate, and number of coats. Accurate estimation helps you buy the right amount—avoiding costly overages or frustrating mid-project store runs.
| Paint Type | Coverage (sq ft/gal) | Drying Time | Best For |
|---|---|---|---|
| Flat/Matte | 350-400 | 1-2 hours | Ceilings, low-traffic areas |
| Eggshell | 350-400 | 2-4 hours | Living rooms, bedrooms |
| Satin | 350-400 | 2-4 hours | Kitchens, bathrooms, hallways |
| Semi-gloss | 350-400 | 4-6 hours | Trim, doors, cabinets |
| High-gloss | 300-350 | 6-8 hours | High-impact trim, furniture |
| Primer | 200-300 | 1-2 hours | New drywall, stain blocking |
Basic Paint Formula
Where:
- Wall Area= Total paintable surface in sq ft
- Coats= Number of paint coats needed
- Coverage= Square feet per gallon (typically 350-400)
Calculating Wall Area
Calculate the total wall area by finding the perimeter and height, then subtracting openings.
| Surface | Formula | Example |
|---|---|---|
| Room walls | Perimeter × Height | (2×12 + 2×10) × 8 = 352 sq ft |
| Single wall | Length × Height | 15 × 8 = 120 sq ft |
| Ceiling | Length × Width | 12 × 10 = 120 sq ft |
| Door (subtract) | ~21 sq ft each | Standard 3' × 7' door |
| Window (subtract) | ~15 sq ft each | Average window size |
| Trim (add) | Linear feet × width | 120 LF × 0.5' = 60 sq ft |
Wall Area Calculation
Where:
- Perimeter= Distance around room
- Height= Wall height (typically 8')
Factors Affecting Paint Coverage
Actual coverage varies significantly based on surface conditions and paint application method.
| Factor | Effect on Coverage | Adjustment |
|---|---|---|
| Smooth drywall | Maximum coverage | Use label estimate |
| Light texture | Reduced 10-15% | Add 10-15% paint |
| Heavy texture | Reduced 20-30% | Add 20-30% paint |
| Porous surface | Reduced 20-40% | Prime first |
| Dark to light color | Extra coats needed | Add 1-2 coats |
| Sprayer application | Uses 20-30% more | Calculate extra |
| Roller application | Standard coverage | Use label estimate |
| Brush only | Slightly less efficient | Add 5-10% |
Pro tip: Buy paint with a built-in primer when covering dark colors or new surfaces—it often requires fewer total coats.
How Many Coats Do You Need?
The number of coats depends on the color change and surface condition.
| Situation | Coats Recommended | Notes |
|---|---|---|
| Same or similar color | 1-2 | Touch-up or refresh |
| Light to light color | 2 | Standard repaint |
| Dark to light color | 2-3 + primer | Tinted primer helps |
| Light to dark color | 2 | Tint primer to dark |
| New drywall | 1 primer + 2 | Seal porous surface |
| Stained surfaces | Stain-block primer + 2 | Water stains, smoke |
| Exterior wood | 1 primer + 2 | Weatherproofing |
Quality matters: Premium paints often achieve better coverage in fewer coats, potentially offsetting their higher cost.
Understanding Paint Quantities
Paint is sold in standard sizes. Calculate your needs and round up to the next available size.
| Container Size | Coverage (approx) | Best For |
|---|---|---|
| Sample/quart (32 oz) | 75-100 sq ft | Testing, small touch-ups |
| 1 gallon | 350-400 sq ft | Small rooms, accent walls |
| 5 gallons | 1750-2000 sq ft | Large rooms, whole house |
| Test pot (8 oz) | ~25 sq ft | Color testing only |
Cost tip: 5-gallon buckets often cost less per gallon than individual gallons. Calculate if you need 3+ gallons; buying a 5-gallon may be more economical.
Paint Estimates by Room Type
Quick estimates for common room sizes (2 coats, standard ceiling height, average openings deducted).
| Room Type | Typical Size | Wall Paint | Ceiling Paint | Trim Paint |
|---|---|---|---|---|
| Small bedroom | 10×10 ft | 1 gallon | 0.5 gallon | 1 quart |
| Average bedroom | 12×12 ft | 1.5 gallons | 0.5 gallon | 1 quart |
| Master bedroom | 14×16 ft | 2 gallons | 1 gallon | 1-2 quarts |
| Bathroom | 5×8 ft | 1 gallon | 1 quart | 1 quart |
| Kitchen | 12×14 ft | 1.5-2 gallons | 0.5-1 gallon | 1 quart |
| Living room | 15×20 ft | 2-3 gallons | 1-1.5 gallons | 1-2 quarts |
Whole house estimate: A 2,000 sq ft home typically needs 12-15 gallons for walls (2 coats), plus ceiling and trim paint.
Exterior Paint Calculation
Exterior surfaces have different considerations than interior work.
| Surface | Coverage (sq ft/gal) | Special Considerations |
|---|---|---|
| Smooth siding | 350-400 | Standard coverage |
| Rough wood siding | 200-300 | Texture absorbs paint |
| Stucco | 150-200 | Very porous, needs primer |
| Brick | 150-200 | Porous, may need 2 coats primer |
| Concrete/masonry | 200-300 | Use masonry paint |
| Metal siding | 350-400 | Prime bare metal first |
Weather factor: Don't paint exterior surfaces when temperatures are below 50°F or above 90°F, or when rain is expected within 24 hours.
Worked Examples
Calculate Paint for a Bedroom
Problem:
A 12×14 foot bedroom with 8-foot ceilings has 1 door and 2 windows. How much paint is needed for walls (2 coats)?
Solution Steps:
- 1Calculate perimeter: 2×(12+14) = 52 linear feet
- 2Calculate gross wall area: 52 × 8 = 416 sq ft
- 3Subtract openings: 1 door (21 sq ft) + 2 windows (30 sq ft) = 51 sq ft
- 4Net wall area: 416 - 51 = 365 sq ft
- 5For 2 coats: 365 × 2 = 730 sq ft needed
- 6At 350 sq ft/gallon: 730 ÷ 350 = 2.09 gallons
Result:
Purchase 2.5-3 gallons of wall paint. Buying 3 gallons ensures enough for touch-ups and accounts for coverage variations.
Calculate Paint for Textured Walls
Problem:
A living room is 15×20 feet with knockdown texture and 9-foot ceilings. Going from dark blue to light gray.
Solution Steps:
- 1Calculate perimeter: 2×(15+20) = 70 linear feet
- 2Calculate gross area: 70 × 9 = 630 sq ft
- 3Estimate openings (2 doors, 4 windows): 42 + 60 = 102 sq ft
- 4Net area: 630 - 102 = 528 sq ft
- 5Texture adjustment (+20%): 528 × 1.20 = 634 sq ft per coat
- 6Dark to light needs 3 coats: 634 × 3 = 1902 sq ft coverage
- 7Gallons needed: 1902 ÷ 350 = 5.4 gallons
Result:
Purchase a 5-gallon bucket plus 1 gallon (6 gallons total). Consider tinted primer to reduce topcoats needed.
Whole Room Calculation (Walls, Ceiling, Trim)
Problem:
Paint a 10×12 foot room—walls (blue), ceiling (white), and trim (white). Standard 8-foot ceilings.
Solution Steps:
- 1Walls: Perimeter (44 ft) × 8 = 352 sq ft, minus openings (~35 sq ft) = 317 sq ft
- 2Walls (2 coats): 634 sq ft ÷ 350 = 1.8 gallons → 2 gallons blue
- 3Ceiling: 10 × 12 = 120 sq ft, 2 coats = 240 sq ft ÷ 400 = 0.6 gallons → 1 gallon white (flat)
- 4Trim (doors, baseboards, crown): Estimate 80 sq ft × 2 coats = 160 sq ft → 1 quart semi-gloss
- 5Total: 2 gal wall, 1 gal ceiling, 1 qt trim
Result:
Buy 2 gallons wall paint (blue), 1 gallon ceiling paint (flat white), 1 quart trim paint (semi-gloss white).
Tips & Best Practices
- ✓One gallon of paint covers approximately 350-400 square feet on smooth surfaces.
- ✓Always calculate for 2 coats minimum—one coat rarely provides proper coverage.
- ✓Subtract 21 sq ft per door and 15 sq ft per window from your wall area.
- ✓Textured walls need 20-30% more paint than smooth surfaces.
- ✓Buy extra paint for touch-ups and store it properly for years of use.
- ✓5-gallon buckets are more economical when you need 3+ gallons of the same color.
- ✓Quality paint covers better and lasts longer—it often requires fewer coats.
Frequently Asked Questions
Sources & References
Last updated: 2026-01-22