Coverage without the guesswork
Paint Calculator
How much paint do you need? Estimate wall and ceiling paint, primer, and painting supplies for one room or a whole project. Compare container sizes and build a materials budget with sales tax.
How to calculate how much paint you need
- Measure each room. Enter length, width, and wall height for a rectangular room. For a single wall or irregular layout, choose total wall length. Add more rooms as needed.
- Subtract unpainted openings. Add together the areas of doors, windows, and other wall surfaces you will not paint. Select the ceiling if it is part of the project.
- Set coats and coverage. Enter the coverage printed on each paint or primer label. Adjust the extra allowance for application losses and touch-ups.
- Plan your purchases. Enable available container sizes and enter their prices. Choose lowest material cost or least leftover paint.
- Finish the budget. Add tape, rollers, brushes, and other supply costs, enter sales tax, then export or print the shopping list.
Dimensions can be entered in feet or meters; changing units converts your existing measurements. Coverage always uses square feet per US gallon, and purchase quantities use US gallons. All walls share one paint, ceilings use a separate paint, and primer covers all selected surfaces. Run separate projects for different wall colors or products.
Paint coverage and wall area formulas
Calculate the surface area first, deduct openings, then account for coats and allowance. A room's floor area alone does not tell you its wall area.
Net wall area = wall area − unpainted openings
Ceiling area = length × width
Paint gallons = net area × coats × (1 + allowance ÷ 100) ÷ coverage
For custom wall lengths, wall area is total wall length × height. Enter a separate ceiling area when needed. Openings are deducted from walls once, before coats are applied; they do not reduce the ceiling area.
Primer uses the same gallons formula with its own coverage and coat count. Adding primer does not automatically reduce finish coats. The default 350 ft² per gallon for paint is an editable assumption; use your product label and adjust for the surface and application method.
Example: paint for a 12 × 10 foot room
For a room 12 feet long, 10 feet wide, and 8 feet high, the walls total 352 square feet. Subtract 42 square feet of doors and windows to leave 310 square feet of paintable walls.
= approximately 1.95 US gallons
With a 10% allowance and coverage of 350 ft² per gallon, two one-gallon cans cover this wall estimate. If you also paint the 120-square-foot ceiling with two coats at the same coverage and allowance, it needs approximately 0.75 US gallons, purchased separately from the wall paint.
The purchase planner uses the unrounded requirement, not the displayed two-decimal value. Container recommendations depend on the enabled sizes and your entered prices. This example illustrates the calculation rather than a guarantee of actual coverage.
Estimate painting materials and supply costs
Your budget includes the recommended wall paint, ceiling paint, optional primer, entered supplies, and sales tax. Supply quantities are independent of room area: enter only what you need to buy and leave items you already own at zero.
- Masking or painter's tape, drop cloths, and plastic sheeting
- Roller covers, frames, extension poles, trays, and liners
- Brushes, sandpaper, patching materials, and other supplies
Materials subtotal = paint + primer + supplies
Estimated total = materials subtotal + sales tax
Enter local product prices in USD; the defaults are editable examples. The same entered sales tax rate applies to paint and supplies. Labor, delivery, and other contractor charges are excluded, so this is a materials estimate rather than a painting-service quote.
The lowest-cost option can buy extra paint when a larger container costs less. The least-leftover option prioritizes purchased volume, then cost. Wall paint, ceiling paint, and primer are rounded separately. Reported liquid weight excludes containers and supplies.
Paint calculator FAQs
How much paint does one gallon cover?
This calculator starts at 350 square feet per US gallon per coat. Two coats at that coverage use one gallon per 175 square feet before allowance. Replace the default with your product label's coverage.
Should I subtract doors and windows?
Enter the combined area of openings you will not paint. Multiply each opening's width by its height, then add the areas together using the selected units. The calculator deducts this area from walls before multiplying by coats.
Can I estimate ceiling paint and primer separately?
Yes. Select each ceiling you plan to paint and set ceiling coverage and coats independently. Enable primer to estimate it across all selected walls and ceilings using its own coverage and coat count.
Which measurements should I enter?
Measure each room separately. Use total wall length for an irregular layout or a single wall. For openings, enter the combined area of doors and windows you will not paint. Different-height walls can be separate entries.
How much coverage should I use?
The default 350 square feet per gallon is a starting assumption. Replace it with your paint label’s coverage and account for surface texture and application method. Ceiling paint and primer have independent coverage settings.
Are projects saved?
Your latest valid project is saved in this browser when local storage is available. Room names and measurements remain on your device. CSV and print exports include the current estimate. Reset removes the saved project and starts fresh.
What is included in the budget?
Selected paint and primer containers, entered supply quantities and prices, and your sales tax. Include brushes, rollers, tape, protective coverings, and repair materials in the supplies section. Delivery and labor are excluded. Prices, coverage, and liquid weights are editable planning assumptions.
