Wall Paint Calculator

Dedicated interior wall paint calculator. Enter room dimensions to compute perimeter, gross wall area, opening deductions, net wall area, and gallons required with waste.

ft

Interior length of the room.

ft

Interior width of the room.

ft

Floor-to-ceiling height. Standard: 8 ft.

Standard interior doors (~3×7 ft = 21 sq ft each).

Standard windows (~3×5 ft = 15 sq ft each).

Most walls need 2 coats. Covering dark colors may need 3.

sq ft/gal

Square feet per gallon. Default 350 is manufacturer average.

%

Extra for roller waste, spills, touch-ups. Default 10%.

How this calculator works

This calculator is dedicated to interior wall painting — it follows the painter's workflow precisely:

  1. Perimeter: 2 × (room length + room width).
  2. Gross wall area: perimeter × wall height.
  3. Opening deductions: subtract doors (21 sq ft each) and windows (15 sq ft each).
  4. Net wall area: per-coat paintable surface.
  5. Paint required: net area × coats ÷ coverage rate.
  6. Recommended purchase: gallons + waste allowance, rounded to nearest quart.

This differs from the general Paint Calculator by focusing on the perimeter-first workflow that painters use. For ceiling jobs, use the Paint Calculator (ceiling area = room length × width).

Formula

perimeter        = 2 × (room_length + room_width)
gross_wall_area  = perimeter × wall_height
door_area        = doors × 21 sq ft
window_area      = windows × 15 sq ft
deductions       = door_area + window_area
net_wall_area    = gross_wall_area − deductions
total_paintable  = net_wall_area × coats
gallons          = total_paintable / coverage
recommended      = gallons × (1 + waste_pct / 100)
  rounded up to nearest quart (0.25 gal)

Example

For a 12 × 10 ft room with 8 ft ceilings, 1 door, 2 windows, 2 coats, 350 sq ft/gal, 10% waste:

  • perimeter = 2 × (12 + 10) = 44 ft
  • gross_wall_area = 44 × 8 = 352 sq ft
  • deductions = 21 + 30 = 51 sq ft
  • net_wall_area = 352 − 51 = 301 sq ft
  • total_paintable = 301 × 2 = 602 sq ft
  • gallons = 602 / 350 = 1.72 gallons
  • recommended = 1.72 × 1.10 = 1.89 → 2 gallons

Important assumptions

  • Standard interior door: 3 × 7 ft = 21 sq ft.
  • Standard window: 3 × 5 ft = 15 sq ft.
  • Default coverage: 350 sq ft/gallon (manufacturer average for interior wall paint).
  • Default waste 10% — covers roller absorption, spills, touch-ups.
  • This calculator estimates WALLS only. For ceiling paint, use the general Paint Calculator.
  • For textured walls, increase waste to 15%.
  • Primer is separate (200-300 sq ft/gal typical).

FAQ

How is this different from the Paint Calculator?
The Wall Paint Calculator is dedicated to interior wall painting and shows the perimeter-first workflow painters use. The general Paint Calculator includes broader context (ceiling calculation guidance, total surface area breakdown). Both produce the same gallon estimate for the same inputs.
How do I calculate paint for just one wall?
Multiply the wall's length × height to get the area, subtract any doors/windows on that wall, then divide by your coverage rate. This calculator handles all 4 walls of a rectangular room automatically.
Should I paint the ceiling the same color?
Ceilings are usually painted with flat-finish white paint, separate from wall paint. Calculate ceiling area as room length × width, then divide by coverage (typically 400 sq ft/gal for flat ceiling paint).
How much extra paint should I keep for touch-ups?
Save 1 quart per room for touch-ups. Label the can with the room name, color code, and date. Most paint is good for 2-5 years if sealed properly.
Can I use this for painting kitchen or bathroom walls?
Yes, but use kitchen/bathroom paint (mold-resistant, scrubbable). Coverage is similar (350 sq ft/gal) but you may want 3 coats in high-moisture areas for durability.