How to Calculate Paint for Cathedral and Vaulted Ceilings
To measure a vaulted ceiling: multiply floor length by floor width to find floor footprint area, then multiply by the roof slope pitch multiplier (1.054 for 4/12 pitch, 1.118 for 6/12 pitch, 1.202 for 8/12 pitch, or 1.414 for 12/12 pitch). For example, a 16×20 ft room (320 sq ft floor) with a 6/12 pitch vaulted ceiling has 358 sq ft of actual ceiling surface area.
Published 2026-03-01 · Updated 2026-03-01 · 8 min read
Understanding Pythagorean Slope Multipliers
Because cathedral ceilings slope upward at an angle, their surface area is significantly larger than the flat room floor beneath them. Using the Pythagorean theorem (Hypotenuse = √(Rise² + Run²)), roof pitches convert directly into flat area expansion factors.
Worked Example: Great Room with 8/12 Pitch Cathedral Ceiling (18×24 ft floor)
Calculating paint for a cathedral ceiling requiring 2 coats of flat white ceiling paint.
Order 3 gallons of flat ceiling paint to cover both slope planes with 2 complete coats.
How do I determine the pitch of my interior ceiling?
Place a 12-inch level against the slope, hold it level, and measure the vertical distance from the 12-inch mark down to the ceiling. That measurement is your rise over 12 (e.g. 6 inches rise = 6/12 pitch).
Related calculators
Related articles
- How Much Ceiling Paint Do I Need? Square Foot Formula
- How Much Paint Do You Need for a 12x12 Room?
- How to Calculate Exterior Paint Square Footage for Siding
- How Many Gallons of Primer for Bare Drywall?
- How to Calculate Trim and Baseboard Linear Foot Paint
- How Much Paint for Kitchen Cabinets: Door & Box Formula