Home & Construction · Paint planning
Estimate how much paint you need for an interior room, individual walls, a ceiling, exterior walls, or a known paintable area. Account for openings, coats, product coverage, an optional extra allowance, and the container size you plan to buy.
Results
Paint quantity depends on the net paintable area, the number of coats, and the coverage of the specific paint. This calculator keeps those assumptions visible. It first finds paintable area, multiplies by coats, divides by coverage per coat, then applies any extra/touch-up allowance you choose.
For rooms and walls, measured openings can be deducted before coats are applied. The calculator shows the base paint need and any extra allowance separately. It then rounds the planned exact need up to the container size you selected so the purchase quantity is not confused with the mathematical paint requirement.
The US planning default is 350 square feet per US gallon, which converts to about 8.6 square meters per liter. Manufacturer guidance for many smooth-wall paints is often around 350-400 square feet per gallon, but formulation, surface texture, porosity, condition, color change, and application method can materially change coverage. Use the product label when available.
Interior room mode estimates wall area as 2 x (room length + room width) x wall height. It does not include the ceiling. Add measured doors and windows only if you want them deducted from the gross wall area.
Add each wall using its width, height, and quantity. This is useful for rooms that are not simple rectangles, feature walls, or projects where only selected walls will be painted. Up to 100 wall rows are supported.
Ceiling mode uses length x width x quantity. It does not subtract doors or windows. Enter the number of coats and the coverage rate for the ceiling paint you actually plan to use.
Exterior mode totals measured wall rectangles and can deduct measured openings. It does not automatically assume siding type, trim, garage doors, spray loss, rough-surface absorption, or other project-specific factors.
Openings are optional. If you enter them, the calculator subtracts their measured width x height x quantity. If total openings equal or exceed the gross wall area, the calculation is rejected instead of silently clamping the result to zero.
The exact need remains unrounded through the coverage calculation. The purchase recommendation is a separate container-count step. That distinction helps you see why, for example, a 2.75-gallon planned need becomes three 1-gallon containers.
The optional allowance starts at 0%. It is not hidden waste. If you choose an allowance, the calculator shows that extra quantity separately from the base requirement before purchase rounding.
Internally, the calculator uses exact SI conversions: 1 foot = 0.3048 meter, 1 square foot = 0.09290304 square meter, and 1 US gallon = 3.785411784 liters. Switching US and Metric converts current entries instead of discarding them.
This is an estimate, not a guarantee that a quantity will be sufficient. It does not select colors, sheen, paint brands, primer, stain, floor coating, or contractor labor pricing. Rough, porous, repaired, textured, or highly contrasting surfaces can require materially different coverage or additional coats.
The calculation runs in this browser page. This tool does not upload measurements or results, does not require an account, and does not store the project in a database. Copy, CSV, and print/export are initiated locally by you.
Related Apps
If you need to combine several shapes before using Known area here, Square Footage Calculator can total those measured areas without changing the Paint Calculator estimate.
Square Footage CalculatorTotal simple measured areas before bringing the net area into this paint estimate.