Paint Calculator

How this paint estimate works

In Whole room mode, wall area is 2 × (length + width) × height, minus 21 sq ft per door and 15 sq ft per window. Paint needed = net area × coats × (1 + allowance ÷ 100) ÷ label coverage. The result shows both the calculated volume and the containers to buy.

Painting one wall or using a measured area

Choose Single wall to enter wall length, height and the measured area of unpainted openings. A 12 × 8 ft wall with a 21 sq ft door has 75 sq ft to paint. At two coats, 350 sq ft/gal and 10% allowance, it needs 75 × 2 × 1.10 ÷ 350 = 0.47 gallon, covered by two quarts (0.5 gallon).

Choose Known net area if you have already measured the paintable surfaces. For 333 sq ft, two coats at 350 sq ft/gal with 10% allowance need 2.09 gallons. Doors and windows are already excluded, so this mode does not deduct them again. Estimate each product and colour separately.

Separate paint for walls, ceiling and trim

Walls, ceiling, primer, trim enamel, and door paint are separate line items because they may use different products. Open Separate-product shopping list in the calculator to set each layer's coat count, label coverage, and unit price. The result rounds every product independently; leftover wall paint is not treated as available ceiling paint or primer.

• Walls: use net wall area after subtracting doors and windows.
• Ceiling: uses floor area and its own coating assumptions.
• Primer: covers walls and the included ceiling when selected.
• Trim: uses entered linear length × the visible 3-inch planning width.
• Doors: optionally adds one or two 21 sq ft faces per entered door.

Worked example: Five interior spaces

This sample project has two bedrooms, a living room, a kitchen, and a hallway. Each bedroom deducts one 21 sq ft door and two 15 sq ft windows. The other spaces have no opening deductions in this example. Use two coats, 350 sq ft/gal coverage, and 10% allowance; replace these assumptions with your measurements and product label.

Total paintable area: 2,258 sq ft. If one product and colour suits all these walls and the ceiling, the combined requirement is 2,258 × 2 × 1.10 ÷ 350 = 14.19 calculated gallons. Buying three five-gallon buckets leaves about 0.81 gallon for touch-ups. At an example price of $42 per gallon, that purchase costs $630.

For different wall and ceiling products, calculate each purchase separately: 2,034 × 2 × 1.10 ÷ 350 = 12.79 gallons for the walls, and 224 × 2 × 1.10 ÷ 350 = 1.41 gallons for the ceiling. Use each product's own coverage and round by product and colour in the shopping list.

Choose coverage for your surface

Compare product examples in the coverage reference chart. For brick and stucco, use the masonry paint calculator.

Common paint container sizes

For two complete coats, halve the area before adding application allowance. The project type does not determine the quantity: measure the surfaces and use the selected product's coverage.

How should you round the result?

Paint is sold in fixed container sizes, so the calculated volume must be rounded to containers available locally. For example, 2.3 gallons can be covered by two one-gallon cans and two quart cans. A small surplus from the same batch is useful for touch-ups; compare unit prices, tinting rules, storage needs, and return policies before choosing a five-gallon bucket.

What changes the estimate?

• Preparation: Estimate any required primer separately from finish paint.
• Colour change: Enter the coats needed for an even colour, as well as the product's spread rate.
• Application: Allow for spray loss and paint left in brushes, rollers, and trays. Check whether the published coverage already includes that loss.
• Texture: Use coverage specified for the actual surface, including its recesses and profile.
• Product: Read the chosen paint's label or technical data for coverage, preparation, and drying conditions.

Frequently asked questions

Should I buy extra paint "just in case"?

Yes — we recommend 10–15% extra. Different paint batches can vary slightly in colour, and you will need some for future touch-ups. Our calculator includes a 10% waste allowance by default.

What if I measure my room wrong?

Measure length and width at floor level and check wall height in at least two places. Keep measurements in one unit system and record opening deductions separately. Round the final purchase into available containers after calculating the required volume.

One coat or two coats?

Two coats are the calculator's planning starting point. A same-colour refresh may need only one, while a larger colour change may need primer or additional finish coats. Follow the selected coating system and check a small test area before reducing the planned coat count.

Does paint quality affect coverage?

Coverage varies by formulation, substrate, film thickness, and application. A higher price does not establish a higher spread rate. Use the chosen product's label coverage and estimate hiding with a separate coat count.

Can I use the same paint for walls and ceiling?

Ceiling paint is formulated differently — flatter sheen, less dripping, and often thicker. Plan it independently with the ceiling paint calculator when the product, coverage, colour, or coat count differs from the walls.

Example: a 12 × 12 room

A 12 ft by 12 ft room with 8 ft walls has 384 sq ft of gross wall area. Subtract one door (21 sq ft) and two standard windows (30 sq ft) to get 333 sq ft of net wall area. Two coats at 350 sq ft per gallon with 10% waste require 2.09 gallons, so plan to buy 2 one-gallon cans plus 1 quart can (2.25 gal total).

Common room-size estimates

Before you buy

• Check the coverage and coat instructions on the product label.
• Use a lower coverage rate for textured or porous surfaces (see table above).
• Calculate repairs, stains, new drywall, or major colour changes separately with the primer calculator.
• Calculate doors, trim, cabinets and ceilings separately when they use different products or colors.
• Buy all paint for one colour at the same time to ensure batch consistency.
• Store leftover paint properly: seal the lid tightly and keep in a cool, dry place.