Running out of paint mid-wall or buying three extra gallons you’ll never use — both are frustrating and wasteful. Our Paint Calculator tells you exactly how much paint you need based on your room’s dimensions, number of coats, and surface type. Save money and time with a precise estimate before your next paint job.
Paint Calculator
Room Paint Calculator
How Much Paint Does a Room Need?
The standard rule of thumb is that one gallon of paint covers approximately 350–400 square feet with one coat on a smooth, previously painted surface. For new drywall or porous surfaces, expect closer to 300 sq ft per gallon.
Paint Coverage by Surface Type
| Surface | Coverage per Gallon | Notes |
|---|---|---|
| Smooth drywall (primed) | 350–400 sq ft | Standard estimate |
| New/unprimed drywall | 200–300 sq ft | Always prime first |
| Textured walls | 250–300 sq ft | More surface area |
| Wood/trim | 400–450 sq ft | Smooth, low absorption |
| Brick/masonry | 75–150 sq ft | Highly porous |
How to Calculate Paint Needed – Step by Step
- Calculate total wall area: Add up the area of all four walls (length × height for each wall).
- Subtract doors and windows: Each standard door = ~20 sq ft; each average window = ~15 sq ft.
- Multiply by number of coats: Most jobs require 2 coats for even coverage.
- Divide by coverage rate: Use 350 sq ft/gallon for a standard estimate.
- Add 10% buffer: Always buy a bit extra for touch-ups.
Paint for Ceiling and Trim – Separate Calculation
Our calculator estimates wall paint only. Don’t forget:
- Ceiling: Length × Width ÷ 350 gallons (ceiling paint is thicker, covers more)
- Trim/baseboards: About 1 quart per average room for baseboards and window trim
- Doors: One quart covers both sides of a standard interior door
How Many Coats of Paint Do You Need?
- Same color refresh: 1 coat may suffice if the surface is clean and primed
- Color change (light to dark): 2 coats minimum
- Dark to light (e.g., red to white): 3 coats — use a tinted primer
- New drywall: 1 coat primer + 2 coats paint
Frequently Asked Questions
How much does a gallon of paint cost?
Interior latex paint ranges from $25–$75 per gallon depending on brand and finish. Premium paints (Benjamin Moore, Sherwin-Williams) often cover better in one coat, potentially saving you money overall.
Should I buy paint in gallons or quarts?
If you need more than 1.5 quarts, a gallon is always more economical. Buy extra in the same batch/color code — paint mixed in different batches can have slight color variations.
Does paint finish affect coverage?
Flat/matte finishes absorb more paint; glossy finishes cover more area per gallon. For most walls, an eggshell or satin finish offers the best balance of coverage and durability.
How long does leftover paint last?
Latex paint stored in a sealed container at room temperature lasts 2–10 years. Use a paint key to seal the lid tightly and store upside down to prevent skin formation.