How Much Paint Do I Need? A Guide to Accurate Estimation
A fresh coat of paint is one of the quickest and most cost-effective ways to completely transform a space. But before you start taping edges and laying down drop cloths, the most important question to answer is: "How much paint do I actually need?" Buying too little leads to frustrating mid-project trips to the store—where you risk not finding a perfect color match—while buying too much is a waste of money. This paint calculator is designed to give you a reliable estimate, ensuring you can start your project with confidence and the right amount of supplies.
The Formula for Calculating Paint Needs
Estimating paint isn't complicated. The process involves finding the total paintable area of your room and then dividing that by the coverage of a single gallon of paint.
- Calculate Wall Area: Find the perimeter of your room by adding the lengths of all walls together. For a rectangular room, the formula is `(Length + Width) × 2`. Multiply this perimeter by the wall height to get the total wall area.
- Subtract Doors and Windows: Unlike when estimating drywall, you should subtract the area of doors and windows, as you won't be painting them. This calculator uses standard sizes (21 sq ft for a door, 15 sq ft for a window) to simplify this step.
- Add Ceiling Area (Optional): If you're painting the ceiling, calculate its area (`Length × Width`) and add it to your wall total.
- Account for Multiple Coats: One coat is rarely enough, especially when covering a darker color. Most projects require at least two coats for a smooth, professional finish. Multiply your total paintable area by the number of coats you plan to apply.
- Divide by Paint Coverage: A general rule of thumb is that one gallon of paint will cover approximately 350 to 400 square feet. This calculator uses a conservative estimate of 350 sq ft per gallon to be safe.
Gallons Needed = (Total Paintable Area × Number of Coats) / 350
Tips for a Professional-Looking Paint Job
Getting the quantity right is just the start. For the best results, consider the surface you're painting. New, unprimed drywall is very porous and will soak up a lot of paint. It's highly recommended to apply a coat of primer first, which you can also estimate using this calculator. If you've just installed new walls, our Drywall Calculator can help ensure you have the right amount of material for that stage, too.
Choosing the right paint sheen (e.g., matte, eggshell, satin) also impacts the final look and durability. For in-depth advice on selecting the perfect paint and sheen for your project, major brands like Sherwin-Williams offer extensive project centers with tips and inspiration. Always remember that proper prep work—cleaning walls, patching holes, and taping edges—is the true secret to a flawless finish.