Primary material
9 1-gal cans
Exterior paint gallons
Use the calculated gallon count as your buying starting point, then verify siding material, sheen, tint base, and label coverage.
Exterior paint calculator
Exterior paint calculator for siding, gables, doors, and windows.
Estimate house exterior paint from siding area, gable ends, door and window deductions, coats, primer, coverage, and extra allowance before comparing gallons and 5-gallon pails.
Quick exterior paint answers
Common house checks
30 x 40 ranch, 2 coats
9 gal
2 five-gal pails
8.93 gal calculated
24 x 36 small house, 2 coats
7 gal
2 five-gal pails
6.73 gal calculated
40 x 50 two-story, 2 coats
24 gal
5 five-gal pails
23.37 gal calculated
Shopping list
Compare exterior paint, primer, and prep supplies
Large jobs
2 5-gal pails
5-gal exterior paint pails
For whole-house siding jobs, compare total gallons against 5-gallon pail pricing and color consistency.
Optional primer
0 1-gal cans
Exterior primer
Use primer for bare wood, patched siding, stains, masonry, chalky surfaces, and strong color changes.
Prep and application
Scraper, caulk, roller, and sprayer prep
Exterior paint jobs often need scraping, sanding, caulk, masking, drop cloths, rollers, brushes, and sprayer prep.
Formula shown
How exterior paint estimates work
Siding and gable area
walls = perimeter x wall height; each gable = width x rise / 2
Openings and coats
paintable area = walls + gables - doors x 21 - windows x 15
Gallons to buy
gallons = paintable area x coats x allowance / coverage per gallon
Sources
- BEHR How Much Exterior Paint to Buy — exterior paint coverage range and buying guidance
- Lowe's Paint Calculator — paint and primer coverage ranges and calculator structure
- Sherwin-Williams Paint Calculator FAQ — gallon and primer coverage reference
- HowStuffWorks Estimating Exterior Paint — perimeter, height, openings, and gable estimating method
- The Home Depot BEHR Exterior Paint — retail 1-gallon exterior paint product and coverage context
Reviewed for estimating accuracy
Last updated: June 21, 2026
Estimate only.
This calculator is not a quote. Verify product yield, price, delivery minimums, and local conditions with your supplier or contractor before buying materials.
Perimeter
140 ft
Around the house footprint.
Wall area
1,260 sq ft
Before openings and gables.
Gables
180 sq ft
Triangular wall area.
Openings removed
222 sq ft
Doors and windows.
Related paint tools
Painting rooms or interior trim?
Interior walls and trim use different formulas, so use the focused calculator for that job.
FAQ
Exterior paint calculator questions
Quick answers for house exterior paint gallons, gables, siding coverage, primer, doors, and windows.
How much exterior paint do I need? + -
Measure the house length, width, wall height, gable rise, doors, and windows. The calculator estimates siding area, subtracts openings, multiplies by coats and allowance, then divides by coverage per gallon.
How many square feet does a gallon of exterior paint cover? + -
Many exterior paints list about 250 to 400 square feet per gallon per coat. Rough siding, stucco, masonry, repairs, and sprayer loss can push coverage lower.
Should I include gables? + -
Yes if the triangular gable ends are being painted with the siding. This calculator estimates each gable as width times rise divided by two.
Should I subtract windows and doors? + -
Subtracting openings gives a tighter siding estimate. This calculator uses 21 square feet per exterior door and 15 square feet per window as planning shortcuts.
When do I need exterior primer? + -
Use primer for bare wood, patched siding, stains, masonry, chalky surfaces, and major color changes. Turn on primer when the job needs a separate primer coat.