Ceiling Paint Calculator
Enter the room length and width and choose your ceiling texture. The calculator applies the correct surface multiplier (+20% for knockdown, +30% for popcorn) and rounds up to whole gallons.
Ceiling Size
How ceiling paint math works
Step 1 — ceiling area
ceiling_area = length × width No door or window deductions for ceilings — the entire footprint is painted.
Step 2 — texture adjustment
effective_area = ceiling_area × texture_multiplier Smooth = ×1.0 (no adjustment). Textured/knockdown = ×1.20 (20% more paint for the 3D surface). Popcorn/heavy = ×1.30 (30% more for genuine heavy texture).
Step 3 — gallons
gallons_to_buy = ⌈ (effective_area × coats) ÷ coverage ⌉ Why ceilings need a separate calculation
Ceiling paint covers a flat rectangle (length × width) with no door or window deductions — the entire footprint is painted. The key difference from wall calculations is the texture multiplier: a smooth flat ceiling uses ×1.0, a knockdown or orange-peel texture uses ×1.20, and genuine popcorn/heavy texture uses ×1.30. This accounts for the extra 3D surface area that flat-footprint measurements understate.
Coverage for ceiling flat paint is the same range as wall paint — 300–400 sq ft/gal — because the chemistry is similar. The default 350 sq ft/gal is the conservative working figure cited by Clare, This Old House, and Sherwin-Williams.
Typical ceiling paint amounts by room size
- 10×10 room: 100 sq ft — 1 gallon covers 2+ coats at 350 sq ft/gal
- 12×12 room: 144 sq ft — 1 gallon covers 2 coats (288 sq ft < 350)
- 15×20 room: 300 sq ft — 1 gallon for 1 coat, 2 gallons for 2 coats
- 20×25 room: 500 sq ft — 2 gallons for 1 coat, 3 gallons for 2 coats
Frequently Asked Questions
Ceiling paint is formulated differently: it is thicker (reduces drips when rolling overhead), has a flat finish (hides roller marks and imperfections), and is usually bright white. While wall paint can be used on a ceiling in a pinch, purpose-made ceiling paint gives a better, more professional result.
This calculator adds 20% for knockdown/textured ceilings (×1.20) and 30% for genuine popcorn/heavy texture (×1.30). These multipliers account for the actual 3D surface area being greater than the flat footprint. Very heavy or aged popcorn may need even more — consider adding 10% on top as a safety buffer.
For L-shaped ceilings, measure each rectangle separately and add the two areas. Enter the total as length × 1 with width = total square footage, or calculate each rectangle's gallon count separately and add. The square footage paint calculator on this site accepts direct sq ft entry for unusual shapes.
New drywall and repaired ceilings (after water damage, for example) need primer. The primer calculator on this site gives you the primer gallon count using 200–300 sq ft/gal — less than topcoat because bare drywall is porous. A sealed, previously painted ceiling in good condition usually does not need primer.
Ceiling paint covers the entire ceiling footprint (length × width). Unlike walls, there are no standard openings to deduct. If your ceiling has a skylight, measure its area (width × length of the skylight) and subtract it from the total ceiling sq ft before entering it as the dimensions.