Paint Calculator – How Many Gallons Do You Need?
What Is a Paint Calculator?
Use this paint calculator to quickly estimate how many gallons of paint you need for a room, wall, or entire home. Most interior paint covers 350–400 square feet per gallon.
For example:
• A 12×12 room with 8-foot ceilings needs about 1 gallon per coat.
• A 2,000 sq ft home interior may require 8–12 gallons depending on layout.
• Rough surfaces or textured walls require more paint.
Enter your dimensions below to calculate exact paint quantity and estimated cost.
Our paint calculator estimates wall paint gallons using room size, wall height, coats, and optional deductions for doors and windows.
Inputs
Typical interior paint covers 350–400 sq ft per gallon on smooth walls. Use 350 as a conservative default. Always check your paint can label.
Tip: If you want a quick estimate, leave doors and windows at 0 and increase waste slightly.
Results
Paint Coverage Reference
| Surface Type | Coverage per Gallon |
|---|---|
| Interior Walls | 350–400 sq ft |
| Ceilings | 350 sq ft |
| Exterior Siding | 250–350 sq ft |
| Rough Surfaces | 200–300 sq ft |
Actual coverage varies based on surface texture and number of coats.
Assumptions
- Standard material density assumptions are used where applicable for material estimates.
- Industry standard conversion formulas are used for square footage, gallons, and quarts.
- Waste factor accounts for application loss, touch-ups, and surface texture.
Example
A 12 ft × 10 ft room with 8 ft walls, 2 coats, and 10% waste needs about 2.21 gallons of paint at 350 sq ft per gallon.
Common Room Sizes & Paint Needed (Per Coat)
| Room Size | Wall Area (Approx.) | Gallons Needed |
|---|---|---|
| 10×10 ft | 320 sq ft | 1–2 gallons |
| 10×12 ft | 352 sq ft | 1–2 gallons |
| 12×15 ft | 456 sq ft | 2–3 gallons |
| 15×15 ft | 480 sq ft | 2–3 gallons |
Coverage assumes 350–400 sq ft per gallon.
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Paint Calculator FAQs
How many gallons per room?
A typical 12×12 room with 8-foot walls often needs about 1 gallon per coat, but totals vary by layout and texture.
Should I subtract windows and doors?
Yes. Subtracting windows and doors improves accuracy, especially on rooms with large openings.
How many coats do I need?
Most interior walls need two coats for consistent color and durability.
Do I need primer?
Primer is recommended on new drywall, patched surfaces, or when changing from dark to light colors.
How much extra paint should I buy?
Add about 10% extra for touch-ups, surface variation, and minor measuring error.