Paint Calculator — How Much Paint Do I Need?
Enter your room dimensions to find how many gallons of paint to buy. Add multiple rooms, adjust for doors and windows, choose coats and coverage rating. A 10% waste factor is automatically included.
How to Calculate How Much Paint You Need
Paint coverage is measured in square feet per gallon. To find the amount of paint needed, calculate the total paintable wall area and divide by the coverage rate on the can. Always round up to the next whole gallon and add a 10% waste buffer for cutting in, touch-ups, and uneven surfaces.
The Paint Calculation Formula
Wall area per room = 2 × (Width + Length) × Wall Height Deductions = (No. of doors × 20) + (No. of windows × 15) Paintable area = Wall area − Deductions Gallons needed = (Paintable area ÷ Coverage) × Coats × 1.10 (waste)
Example: A 12 ft × 14 ft room with 8 ft ceilings, 2 doors, 2 windows, 2 coats, standard 350 sq ft/gal paint:
Wall area = 2 × (12 + 14) × 8 = 2 × 26 × 8 = 416 sq ft Doors = 2 × 20 = 40 sq ft Windows = 2 × 15 = 30 sq ft Paintable = 416 − 40 − 30 = 346 sq ft Gallons = (346 ÷ 350) × 2 × 1.10 = 0.989 × 2 × 1.10 = 2.18 → 3 gallons
Paint Coverage Rates by Type
| Paint Type | Coverage | Best For |
|---|---|---|
| Budget / Contractor Grade | 250–300 sq ft/gal | Rental units, one-time use |
| Standard (most mid-range) | 325–375 sq ft/gal | General residential use |
| High-Hide / Premium | 375–400 sq ft/gal | Covering dark colors, one-coat claims |
| Texture / Specialty | 150–200 sq ft/gal | Orange peel, sand finish |
| Primer | 250–350 sq ft/gal | Bare drywall, stain blocking |
How Many Coats Do You Need?
Most interior painting projects require two coats for even, opaque coverage. One coat is sufficient only when painting the same color over existing paint in good condition, or when using a premium "one-coat" formula. Three coats are needed when covering very dark colors with very light ones (e.g., navy blue to white), when painting over repairs or patches, or when using highly saturated accent colors that have low hide.
Interior vs. Exterior Paint Considerations
Interior paint and exterior paint have different formulations even when sold in the same colors. Interior paint is designed for:
- Low VOC (volatile organic compound) content
- Easy cleanup and scrubbing resistance
- Color stability in consistent temperature/humidity
Exterior paint adds UV inhibitors, mildewcides, and flexible resins to handle temperature swings, rain, and direct sunlight. Coverage rates are similar (350–400 sq ft/gal) but exterior paint typically costs $5–$15 more per gallon.
Paint Finishes Explained
| Finish | Sheen Level | Best Rooms | Cleanability |
|---|---|---|---|
| Flat / Matte | None | Ceilings, low-traffic walls | Low |
| Eggshell | Very low | Living rooms, bedrooms | Moderate |
| Satin | Low-medium | Kitchens, bathrooms, hallways | Good |
| Semi-gloss | Medium | Trim, doors, cabinets | Very good |
| Gloss / High-gloss | High | Furniture, accent trim | Excellent |
Tips to Reduce Paint Waste
- Buy paint in the largest available size — a 5-gallon bucket is ~25% cheaper per gallon than individual gallons.
- Tint primer to a shade near the topcoat color — this can reduce wall topcoats from 3 to 2.
- Store leftover paint properly: seal tightly, store upside down briefly to create an air seal, keep between 50°F–80°F. Latex paint lasts 10 years stored properly.
- Mix all cans of the same color together ("boxing") before starting to ensure color uniformity across the project.
Frequently Asked Questions
How many gallons of paint do I need for a 12×14 room?
A 12×14 room with 8-foot ceilings has 4 walls totaling 2×(12+14)×8 = 416 sq ft. Subtract 2 doors (40 sq ft) and 2 windows (30 sq ft) for 346 sq ft of paintable area. At 350 sq ft/gallon with a 10% waste factor and 2 coats: 346 ÷ 350 × 2 × 1.10 = 2.18 gallons — so purchase 3 gallons. Use our calculator above for precise results.
Does paint coverage change for ceilings?
Yes. Ceiling paint typically covers 350–400 sq ft per gallon, similar to wall paint. Ceiling area = room length × width. For the 12×14 example, the ceiling is 168 sq ft — one gallon covers it with a single coat. Note that ceilings are usually painted white and may only need one coat, unlike walls which often need two.
Should I use primer before painting?
Primer is needed when: painting over bare drywall (required — raw drywall absorbs paint), covering dark colors with light ones, painting over glossy surfaces, dealing with water stains, or painting new plaster. If you're going from one similar color to another, a self-priming paint eliminates a separate primer step. Primer costs $15–$30/gallon and the same coverage estimate applies.
What is the difference between interior and exterior paint?
Interior paint is formulated for easy cleaning, low odor, and scrubbability — it stays flexible inside consistent temperatures. Exterior paint contains mildewcides and UV-stabilizers to resist weather, fading, and moisture. Never use interior paint outside; it will peel within one season. Exterior paint can technically go inside but off-gasses longer and is unnecessary. Coverage rates (350–400 sq ft/gal) are similar for both types.
How much does it cost to paint a room?
Paint cost: 2 gallons at $35–$55/gallon = $70–$110 for a medium room. Professional painter labor: $2–$6 per sq ft of paintable area, or $1.50–$3 per sq ft for walls only. A 12×14 room with 8-ft ceilings (about 346 sq ft of wall) typically costs $500–$1,200 professionally painted including labor and materials. DIY saves $400–$1,000 per room in labor.
Related Calculators
- Square Footage Calculator — measure room and total floor area
- Tile Calculator — tiles needed for floors and walls with waste factor
- Flooring Calculator — hardwood, laminate, vinyl, carpet material cost