Why use this calculator
Buying the right amount of paint saves money and reduces waste. Too little paint means extra trips to the store and potential color-matching issues between batches. This calculator accounts for doors, windows, and multiple coats to give you an accurate estimate before you start your project.
How to use it
Select your preferred unit system (metric or imperial). Enter your room's length, width, and ceiling height. Specify the number of doors and windows so they can be subtracted from the paintable area. Choose how many coats you plan to apply, then review the amount of paint needed and estimated cost.
The formula
Wall Area = 2 x (Length + Width) x Height. Paintable Area = Wall Area - (Doors x door area) - (Windows x window area). Total Coverage = Paintable Area x Number of Coats. Paint Needed = Total Coverage / coverage per unit (350 sq ft per gallon or 10 sq m per litre), rounded up.
Worked examples
12x10 ft room, 8 ft ceilings, 1 door, 2 windows, 2 coats
Approximately 2 gallons needed covering 618 sq ft total
3.7x3 m room, 2.4 m ceilings, 1 door, 2 windows, 2 coats
Approximately 6 litres needed covering 57.4 sq m total
When people use it
- Planning a DIY room painting project to buy the right amount of paint
- Estimating paint costs for a full home interior renovation
- Comparing costs between different paint brands based on coverage needs
- Providing material estimates for professional painting quotes
Tips
- Always buy a little extra paint for touch-ups — an extra quart or litre is usually sufficient
- Dark colors over light walls or vice versa may require an additional coat beyond the standard two
- Premium paints often have better coverage and may require fewer coats
- Keep leftover paint stored properly for future touch-ups; note the color code on the lid
Questions people ask
- Why does the calculator use 350 sq ft per gallon / 10 sq m per litre?
- These are industry-standard average coverage rates for interior latex paint on smooth walls. Textured walls, porous surfaces, or heavily pigmented colors may reduce coverage.
- Should I paint the ceiling too?
- This calculator covers wall area only. For ceilings, multiply room length by width to get the ceiling area and divide by the coverage rate for additional paint needed. Ceiling paint is typically a different product than wall paint.
- How many coats of paint do I really need?
- Two coats is standard for most interior painting. You may need three coats when making drastic color changes (dark to light or vice versa), painting over patches or repairs, or using a lower-quality paint with less coverage.