Paint & Wall Calculator
Calculate exactly how many gallons of paint you need. Automatically deducts for doors and windows.
Room Measurements
Standard: 2 coats for best coverage
Your Estimate
Gallons Required
0
gallons of paint
Details
Wall Area Breakdown
The Math Behind the Calculator
Paint Coverage Formula
Gallons = (Wall Area - Deductions) x Coats / 350
Where Wall Area = Perimeter x Height, and 350 sq ft is average coverage per gallon.
Most paint covers approximately 350-400 square feet per gallon on smooth surfaces. We use 350 sq ft as a conservative estimate to ensure you don't run short. Standard deductions are:
- Doors: 20 sq ft each (standard 3' x 7' opening)
- Windows: 15 sq ft each (average window size)
Do You Need Primer?
Skip Primer When...
- Painting over the same or similar color
- Walls are in good condition with no stains
- Using paint with built-in primer (paint + primer)
- Previously painted surface is clean and not glossy
Use Primer When...
- Painting over dark colors with lighter paint
- Covering stains, smoke damage, or water marks
- Painting new drywall or patched areas
- Changing from oil-based to latex paint
- Painting over glossy surfaces
Pro Tip: Tinted Primer
When making a dramatic color change, ask the paint store to tint your primer to match your topcoat color. This can reduce the number of finish coats needed from 3 to 2.
Paint Coverage by Surface Type
| Surface Type | Coverage (sq ft/gal) | Notes |
|---|---|---|
| Smooth Drywall | 350-400 | Best coverage |
| Textured Drywall | 250-300 | Texture absorbs more paint |
| Bare Wood | 300-350 | Primer recommended first |
| Brick | 150-200 | Very porous, needs more paint |
| Concrete/Stucco | 150-250 | Use masonry paint |
| Metal | 400-500 | Non-porous, excellent coverage |
How to Calculate Paint for Vaulted Ceilings
Rooms with vaulted or cathedral ceilings have triangular wall sections above the standard wall height. Here's how to account for them:
For Triangular Wall Sections
Triangle Area = (Base x Height) / 2
- Measure the base of the triangle (wall width)
- Measure the height from where the vault starts to the peak
- Calculate: (Base x Height) / 2
- Add this to your rectangular wall area
Example
A room with 12-foot walls and a vault that rises 4 feet in the center:
- Rectangular portion: 12 x 8 = 96 sq ft (per wall)
- Triangular portion: (12 x 4) / 2 = 24 sq ft (per gable wall)
- Add the triangle area only for walls that have the vault
Pro Painting Tips
Buy Extra
Always buy 10-15% more paint than calculated. You'll need it for touch-ups later, and paint batches can vary slightly in color.
Box Your Paint
Mix all your gallons together in a 5-gallon bucket ("boxing") to ensure consistent color throughout the room.
Ceiling Paint Math
For ceilings, simply multiply Length x Width. Ceiling paint typically covers about 400 sq ft per gallon since it's usually smooth.
Frequently Asked Questions
How many coats of paint do I need?
Two coats is standard for most painting projects. You may need 3 coats when covering dark colors with light paint or when using deep/saturated colors.
What's the difference between flat, eggshell, and semi-gloss?
Flat hides imperfections but is hard to clean. Eggshell offers slight sheen and better washability - great for living areas. Semi-gloss is highly durable and best for kitchens, bathrooms, and trim.
How long should I wait between coats?
Latex paint: 2-4 hours. Oil-based paint: 24 hours. Always check the can for specific manufacturer recommendations.