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Paint Calculator
Estimate wall paint square footage, gallons needed, and material cost for rooms or whole homes
Estimated time
2 min
Project Inputs
Estimate wall paint needed for one room or a whole home with similar room layouts.
1) Choose measurement method
Room dimensions are fastest for rectangular rooms. Wall lengths let you estimate irregular layouts.
Enter each wall segment in feet, separated by commas or spaces, such as 14, 12, 14, 12.
2) Project scope
Most interior paint covers around 300 to 400 square feet per gallon per coat. Use the value listed on your paint can for best accuracy.
sq ft/gal
Enter the shelf price for one gallon. The estimate multiplies rounded gallons by this price.
$
3) Door and window exclusions
Subtract non-painted openings like doors and windows so paint quantity is not overstated.Enter openings for this room using the preset sizes below.
Presets: standard door 3 x 7 (21 sq ft), double door 6 x 7 (42 sq ft), standard window 3 x 5 (15 sq ft), large window 4 x 6 (24 sq ft).
Add extra non-painted square footage per room for built-ins, tile backsplashes, or other surfaces you will skip.
sq ft
How It Works
This calculator estimates wall paint quantity by first finding gross wall area, then subtracting door and window exclusions, then multiplying by coat count.
You can calculate from room dimensions or from custom wall lengths. Whole-home mode multiplies one room profile by the number of similar rooms for quick planning.
Gross wall area = 2 x (Length + Width) x Wall height
Gross wall area = (Sum of wall lengths) x Wall height
Paintable area = Gross wall area - (Door and window exclusions)
Gallons = ceil((Paintable area x Coats) / Coverage), Cost = Gallons x Price per gallon
Gross wall area = 2 x (Length + Width) x Wall height
Gross wall area = (Sum of wall lengths) x Wall height
Paintable area = Gross wall area - (Door and window exclusions)
Gallons = ceil((Paintable area x Coats) / Coverage), Cost = Gallons x Price per gallon
- All dimensions are in feet and square feet.
- Coverage and price assumptions can vary by paint brand, sheen, and wall texture.
- This estimate is for wall paint only and does not include primer, ceilings, or trim.
- Always add a small buffer for touch-ups, waste, and color matching between batches.
Example Calculations
Bedroom repaint
12 x 14 ft room, 8 ft walls, 2 coats, 1 standard door, 2 standard windows, 350 sq ft/gal, $42 per gallon
365 sq ft to paint, 3 gallons rounded, $126 estimated cost
Subtracting openings keeps the gallon estimate realistic for smaller rooms.
Open living area
18 x 16 ft room, 9 ft walls, 2 coats, 1 standard door, 3 large windows, 350 sq ft/gal, $55 per gallon
519 sq ft to paint, 3 gallons rounded, $165 estimated cost
Larger windows can remove enough area to save a full gallon in some layouts.
Whole-home estimate
8 similar rooms, each 12 x 12 ft with 8 ft walls, 2 coats, 1 door + 1.5 windows per room, 375 sq ft/gal, $48 per gallon
2,772 sq ft to paint, 15 gallons rounded, $720 estimated cost
Whole-home mode multiplies room area and preset exclusions by room count.
Frequently Asked Questions
Why does the calculator round gallons up?
Paint is typically sold by whole gallons. Rounding up helps avoid coming up short and leaves a little extra for touch-ups.
What coverage per gallon should I use?
Most interior paints cover about 300 to 400 square feet per gallon per coat. Use the label value from your specific paint for best accuracy.
Should I include ceilings and trim?
This calculator estimates wall paint only. If you plan to paint ceilings or trim, run additional estimates and add those gallons separately.
How should I handle whole-home projects with different room sizes?
Run each room type separately and combine totals, or use an average room size in whole-home mode for a quick planning estimate.
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