Paint Calculator
Measure your rooms, account for openings and coats, and leave with a plan for the paint aisle.
Behind the numbers
How the paint calculation works
For each rectangular room, multiply its perimeter by wall height. Deduct doors, windows and other unpainted areas once, before multiplying by coats. Ceilings use length × width and have a separate paint plan.
Net area = gross area − openings − exclusions
Coated area = net area × coats
Paint needed = coated area × (1 + extra % ÷ 100) ÷ coverage
All calculations keep full precision. The main display rounds informational quantities to two decimals. Whole-container rounding happens after combining sections that use the same paint.
From gallons to containers
Enable the sizes your store sells and enter their actual sizes in US gallons (one US quart = 0.25 gallon). Least leftover selects the smallest sufficient volume, then the fewest containers. Lowest cost requires a price for every enabled size and may purchase more paint to save money. Sizes support two decimal places; calculations support up to 1,500 gallons per product.
Wall paint, ceiling paint and primer are separate purchases. Primer, when selected, uses all net wall and ceiling area with its own coats, coverage and allowance. Supplies are checklist items only.
Example: a 12 × 14 ft room
At 8 ft high, the walls total 416 sq ft. One 3 × 7 ft door and two 3 × 4 ft windows remove 45 sq ft, leaving 371 sq ft.
Two coats require 742 sq ft of coverage. With 5% extra and 350 sq ft per US gallon, the requirement is 2.226 gallons. With only 1-gallon cans enabled, buy 3 cans. If quart cans are also enabled, buy 2 one-gallon cans and 1 quart: 2.25 gallons.
Adding the ceiling
The ceiling is 168 sq ft. Two coats, 5% extra and 350 sq ft per gallon require 1.008 gallons of separate ceiling paint, or 2 one-gallon cans. Enter the ceiling product’s own coverage and coats to match your plan.
Other room sizes
With 8 ft walls, no openings, two coats, 5% extra and 350 sq ft per gallon: a 10 × 12 ft room needs 2.112 gallons; a 12 × 12 ft room needs 2.304 gallons. Either rounds to 3 one-gallon cans.
Common paint-planning questions
How much area does a gallon of paint cover?
Use the coverage on the selected product label for your surface and application method. The calculator starts at an editable 350 sq ft per US gallon per coat; it is an example, not a product guarantee.
Should I subtract doors and windows?
Subtract surfaces you will not paint with this product. Door and window counts use the dimensions you enter. Use excluded area for cabinets or other openings, without counting the same area twice. Ceiling exclusions are entered separately. Switching modes preserves your inputs; only fields shown for the selected mode affect its estimate.
How many coats and how much extra should I allow?
The example uses two coats and 5% extra. Enter the coats and allowance appropriate for your product and application. Extra allowance is separate from the additional paint purchased because containers are sold whole.
Can I combine several rooms or colors?
Add rooms using the same product, color and finish to combine them before container rounding. Different wall colors or interior and exterior products should be estimated separately. The calculator keeps ceiling paint separate from wall paint.
Do I need primer?
Consult the product instructions for your surface and existing finish. Choosing Not sure does not add primer to your purchase. Choosing Yes estimates primer for all included wall and ceiling areas; calculate a separate project if only some areas need primer.
Does exterior mode cover gables, texture and trim?
Exterior mode measures rectangular walls and openings. Add a custom area for a gable (triangle area = width × height ÷ 2). Adjust coverage to the product and surface. Trim, texture and absorption are not modeled automatically.
Why is the cost missing?
A full estimate needs a price for every container included in the shopping list. Blank prices are unknown, while zero means free. Lowest-cost comparison needs prices for all selected sizes, including alternatives not ultimately purchased.