Paint Calculator
* Typical deductions: Door = 21 sq ft, Window = 15 sq ft
Eliminate the guesswork from your next home improvement project. Our professional Paint Calculator helps you determine the exact amount of paint needed for any room, saving you time, money, and multiple trips to the hardware store.
Pro Tip: One gallon of paint typically covers 350-400 sq ft. For best results, always plan for two coats of paint to ensure even coverage and true color depth.
- Calculates net surface area automatically
- Subtracts doors and windows for accuracy
- Real-time cost estimation based on local prices
How to Calculate Paint Needs
Calculating the right amount of paint is a critical step in any renovation project. Buying too little paint leads to inconvenient store runs and potential color mismatches if the batch changes. Buying too much results in wasted money and leftover cans that clutter your storage.
The basic formula involves finding the total square footage of your walls and then subtracting the areas that won't be painted, such as doors, windows, and trim. Once you have the net surface area, you divide it by the paint's coverage rate (usually 350-400 sq ft per gallon) and multiply by the number of coats required.
Using the Paint Calculator
Our calculator simplifies the process by handling the subtractions and coat multiplications for you:
- Enter Room Size: Input the length and width of the room, along with the height of the walls.
- Account for Openings: Enter the number of doors and windows. The tool uses standard averages (21 sq ft per door, 15 sq ft per window) to deduct space.
- Adjust Coatings: Most professional jobs require 2 coats. You can adjust this based on whether you are doing a simple refresh or a major color change.
- Coverage & Price: Check your paint can for the coverage rate. Standard is 350. Add your local price per gallon to see a total cost estimate.
Factors Affecting Paint Coverage
While the math provides a solid baseline, several environmental and material factors can influence how much paint you actually use:
- Surface Porosity: Unpainted drywall, fresh plaster, and textured surfaces absorb more paint than previously painted, smooth surfaces.
- Color Change: Going from a very dark color to a very light one (or vice versa) often requires an extra coat or a specialized primer, which increases the total volume needed.
- Application Method: Spraying paint usually requires more volume than rolling or brushing because of overspray and thicker application layers.
Estimation Examples
Small Bathroom (5' x 8')
Assuming 8' ceilings, 1 door, 0 windows, 2 coats.
- Gross Area: 208 sq ft
- Net Area: 187 sq ft
Need: ~1 Gallon
Large Living Room (20' x 15')
Assuming 9' ceilings, 2 doors, 3 windows, 2 coats.
- Gross Area: 630 sq ft
- Net Area: 543 sq ft
Need: ~3.1 Gallons
Frequently Asked Questions
How much paint is in a standard can?
In the US, a standard can contains 1 gallon (3.78 liters). In many other countries, paint is sold in 2.5L or 5L tins. Our calculator provides estimates in both gallons and liters for convenience.
Should I buy exactly what the calculator says?
It's always wise to round up to the nearest whole gallon or tin. Having a small amount of extra paint is essential for future touch-ups or fixing minor mistakes during the project.
Does the calculator include the ceiling?
This specific tool calculates wall area. If you plan to paint the ceiling the same color, you should add the floor area (Length × Width) to your total square footage before calculating gallons.