Paint Amount Calculator
Buy too little paint and the next gallon never matches. Buy too much and you pay for cans that sit in the garage for a decade. This paint amount calculator gives you an exact gallon figure (and a practical order quantity) for any interior, exterior, or textured project, with standard door and window deductions plus a waste allowance for touch-ups.
How the Paint Amount Calculator Works
The paint amount formula is simple:
Gallons = (Paintable Area x Coats) / Coverage Rate
Where:
- Paintable area = gross wall area minus standard doors (21 sq ft each) and windows (15 sq ft each)
- Coats = number of coats you plan to apply, typically 2
- Coverage rate = square feet a gallon covers on your surface
The calculator adds a waste allowance on top (default 10%) so you have enough for touch-ups, then rounds the total up to the next whole gallon because paint is sold in 1-gallon cans.
Coverage Rates by Surface
These are the coverage rates published on Sherwin-Williams, Benjamin Moore, and Behr data sheets:
| Surface | Coverage per Gallon |
|---|---|
| Interior smooth drywall | 350 sq ft |
| Interior with mild texture | 300 sq ft |
| Exterior primed siding | 300 sq ft |
| Rough stucco or masonry | 200 sq ft |
| Split-face block or brick | 150 sq ft |
| Ceilings (flat) | 350-400 sq ft |
Textured or porous surfaces absorb more paint. If you are painting masonry for the first time, plan on 200 sq ft/gal for the first coat and 250-300 for the second.
Example: 12x14 Bedroom
- Room: 12 x 14 ft, 8 ft ceilings
- Perimeter: (12+14+12+14) = 52 ft
- Gross wall area: 52 x 8 = 416 sq ft
- Openings: 1 door (21 sq ft) + 2 windows (30 sq ft) = 51 sq ft
- Paintable area: 416 - 51 = 365 sq ft
- 2 coats at 350 sq ft/gal: (365 x 2) / 350 = 2.09 gallons
- With 10% waste: 2.29 gallons
- Order: 3 gallons
Three gallons leaves enough paint for touch-ups over the next few years, which is exactly when a scuff or wall repair will need it.
Paint Amount for Common Rooms
| Room Size | Wall Area | Gallons (2 coats, no openings) |
|---|---|---|
| 10 x 10 bedroom | 320 sq ft | 2 |
| 12 x 14 bedroom | 416 sq ft | 3 |
| 14 x 16 master | 480 sq ft | 3 |
| 16 x 20 living room | 576 sq ft | 4 |
| 10 x 14 kitchen | 384 sq ft | 3 |
Exterior Paint Amount
A 2,000 sq ft two-story home has roughly 2,500-3,000 sq ft of exterior wall after subtracting windows and doors. At 300 sq ft/gal and 2 coats:
- (2,750 x 2) / 300 = 18.3 gallons
- With 10% waste: 20.2 gallons
- Order: 21 gallons
That's a typical full-house exterior repaint. At $50/gal that is $1,050 in paint alone, plus primer, caulk, and labor.
When to Add More Coats
- Dark to light color change: plan on 3 coats, or use a tinted primer to cut to 2.
- New drywall: primer coat plus 2 top coats.
- Staining or water damage: stain-blocking primer plus 2 top coats.
- Economy paint (under $20/gal): often needs 3 coats where premium paint needs 2.
Primer Is Separate
The paint amount calculator above handles the top coats. Primer has a different coverage rate (200-300 sq ft/gal) and is calculated as a single extra coat. For most repaints, primer is skipped; for new drywall, bare wood, or after patch repairs, calculate primer separately at 250 sq ft/gal.
Tips for Accurate Paint Amount Estimates
- Measure wall by wall, then add. For vaulted or angled walls, break the shape into a rectangle plus a triangle (base x height / 2).
- Do not forget closets. A 5x7 walk-in with 8 ft ceilings adds 192 sq ft.
- Subtract only the openings you are not painting. Trim and the inside face of doors are usually painted and should not be deducted.
- If you plan to paint the ceiling, calculate ceiling paint separately. Use ceiling area (length x width) at 350 sq ft/gal.
- Always buy in the largest can you need. A 1-gallon can costs more per square foot than the same paint in a 5-gallon bucket.