A fast, private room paint calculator
Planning a renovation or a simple room refresh often starts with one question: how much paint do I need? Buying too little means pausing your project for a hardware store run, while buying too much wastes money and leaves you with half-empty cans to store.
This paint calculator gives you an instant, accurate estimate of the paint volume required for any room. By factoring in your room's dimensions, the number of doors and windows, and whether you are painting the ceiling, it takes the guesswork out of your prep work. Because the tool runs entirely locally in your browser, your measurements are never uploaded or saved. You can quickly adjust numbers on your phone while standing in the paint aisle.
How the wall paint calculator works
Calculating paint requirements by hand involves a few steps of geometry. This tool automates the math so you can focus on picking the right color.
First, the calculator determines the total gross area of your walls by calculating the perimeter of the room (length plus width, multiplied by two) and multiplying that by the room's height.
Next, it subtracts the areas that won't be painted. Instead of asking you to measure every single frame, the tool subtracts standard averages: 1.9 square meters (about 20.4 sq ft) for every door, and 1.5 square meters (about 16.1 sq ft) for every window. If you check the "Include ceiling" box, the calculator adds the room's footprint (length multiplied by width) to your total paintable area.
Finally, the tool multiplies this net area by the number of coats you plan to apply, and divides it by the paint's coverage rate to give you the final volume in liters or gallons.
Understanding the paint coverage calculator
Not all paints spread the same way. The "coverage" input is a crucial part of getting an accurate estimate.
Paint coverage is how much surface area a specific volume of paint can coat effectively. In the Imperial system, this is measured in square feet per gallon (ft²/gal). A standard interior latex paint usually covers about 350 ft²/gal. In the Metric system, coverage is measured in square meters per liter (m²/L), with a standard average being around 10 m²/L.
High-quality paints often have better coverage, meaning you might need fewer cans even if the price per can is higher. Conversely, if you are painting over a very porous surface like fresh drywall, raw wood, or textured masonry, the surface will absorb more liquid, effectively lowering your coverage rate. Always check the manufacturer's label on the tin for the most accurate coverage estimate.
Tips for accurate estimates and buying
Account for multiple coats. Most dramatic color changes—especially painting a light color over a dark one—require at least two coats of paint for an even finish. The calculator defaults to 2 coats, but you can adjust this if you are simply doing a single-coat refresh of the same color.
Don't forget the primer. If you are painting new drywall or making a drastic color shift, you will need a primer. Primer usually has a different coverage rate than standard paint. Run the calculator once for your primer (setting coats to 1) and a second time for your topcoat.
Buy a little extra. The calculator gives you the mathematical exact amount needed based on your inputs. In the real world, you lose paint to the roller, the tray, and accidental drips. It is highly recommended to round up and buy about 10% more than the calculator suggests. This also ensures you have leftover paint from the same batch for future touch-ups.
Compare costs. Once you know exactly how many liters or gallons you need, you can use the Unit Price Calculator to compare different brands and tin sizes to find the most cost-effective option for your project. If you have measurements in different units, you can also use the Square Feet to Square Meters converter to standardize your math.