Paint Calculator
Estimate paint required for a room by perimeter, height, doors, windows, number of coats, and paint coverage rate.
Formula & Explanation
This calculator estimates the amount of paint needed to cover a room's walls. Step 1: Calculate paintable area - Gross area = Perimeter × Height - Deduct door openings (approximately 20 sqft per standard door) - Deduct window openings (approximately 12 sqft per standard window) - Paintable area = Gross area − Doors − Windows Step 2: Calculate gallons needed - Formula: Gallons = (Paintable area × Number of coats) ÷ Coverage per gallon - Example: 280 sqft × 1 coat ÷ 400 sqft/gallon = 0.7 gallons Step 3: Round up to purchase quantity - Purchase cans are typically 1 gallon or 5 gallon sizes - Round up 0.7 gallons to 1 can (1 gallon)
Assumptions
- •Standard interior door opening: approximately 20 square feet (3.5 ft wide × 6 ft tall)
- •Standard window opening: approximately 12 square feet (3 ft wide × 4 ft tall)
- •Coverage per gallon varies by paint type: flat latex ~350-400 sqft/gal, semi-gloss ~350-400 sqft/gal, textured surfaces may require 25-50% more
- •One coat provides minimal coverage; two coats recommended for uniform color and durability
- •Does not account for primer; use primer-calculator for primer estimates
- •Assumes smooth drywall surface; rough or porous surfaces (stucco, textured drywall) require more paint
- •Baseboard trim, crown molding, and closet interiors are not included in this estimate
Example Calculation
A 10×10 ft room (40 ft perimeter) with 8 ft ceilings, one door, two windows, painted with one coat at 400 sqft/gallon coverage requires 0.7 gallons, round up to 1 gallon can.
Inputs
Results
Common Paint Coverage Rates
| surface | coverage | notes |
|---|---|---|
| Smooth drywall, flat finish | 350-400 sqft/gal | Most common interior paint |
| Smooth drywall, semi-gloss | 350-400 sqft/gal | For kitchens, bathrooms |
| Textured drywall | 300-350 sqft/gal | Consumes more paint than smooth |
| Exterior wood siding | 300-400 sqft/gal | Depends on wood type and weathering |
| Stucco, masonry | 200-300 sqft/gal | Porous surfaces require more paint |
| Primer (typical) | 250-350 sqft/gal | Lower coverage than topcoat paint |
Frequently Asked Questions
Related Calculators
Interior Paint Calculator
Calculate interior paint needed by specifying wall area, number of coats, and paint coverage rate for smooth drywall.
Wall Paint Calculator
Calculate paint needed for a single wall by specifying width, height, coats, and coverage rate.
Primer Calculator
Calculate primer needed for bare drywall, stains, color changes, or new construction using area and coverage rate.
Paint Cost Calculator
Calculate total paint project cost by combining paint material, labor, waste, and tax.
Paint Coverage Calculator
Calculate how far your paint will go by entering gallons available, coverage rate, and number of coats.