Paint Calculator

These coverage rates estimate paint needs for purchase planning. Rough surfaces, porous materials, and textured finishes typically need more than the baseline rate.

• Interior coverage: One gallon (3.8 liters) covers about 400 square feet (37 square meters).
• Exterior coverage: One gallon (3.8 liters) covers about 350 square feet (33 square meters).

Rounding up to the nearest gallon or liter leaves room for complete coverage and touch-ups. Real coverage varies with surface condition, primer use, paint quality, sprayer or roller application, and humidity.

The paint calculator computes how much paint an interior or exterior project needs, from wall, ceiling, peak, and trim area net of window and door openings, times the coat count, divided by the coverage rate.

• Interior or exterior. Sets the coverage rate used for the estimate: 400 square feet per gallon for interior, 350 for exterior.
• Units. Imperial or metric, matching how the project's measurements were taken.
• Wall dimensions. Width and height per wall; a peak adds a rise measurement for a gabled wall, since the triangular area above the rectangle is not covered by width times height alone.
• Windows and doors. Subtracted from the paintable wall area, since an opening carries no paint.
• Trim. Baseboards, crown molding, and other custom runs that need their own paint, added into the total area alongside the walls.
• Ceilings. Entered separately by length and width, and reported separately from wall paint in the results.
• Coats. Set to reflect primer, base, and finish coats together, since each coat multiplies the paint needed.

Formulas: Wall area uses Area = Width × Height; peak area uses 0.5 × Width × Rise. Paint required equals Total Area ÷ Coverage Rate, multiplied by the number of coats. Results round to the nearest quart in Imperial and to two decimal places in Metric.

Accurate paint estimates plan budgets and reduce waste on real projects. The scenarios below compare coat counts, unit systems, and surface types side by side.

• A full interior room with several walls and a ceiling totals in one pass.
• An exterior facade subtracts its doors and windows from the paintable area before the exterior coverage rate applies.
• Trim, baseboards, chair rails, and crown molding add into the total area alongside the walls.
• Single-coat, two-coat, and primer-plus-finish plans compare side by side for material budgeting.
• Imperial and metric units switch to match local standards or a supplier's specifications.

These examples model common rooms as a starting point, adjusted to match the space at hand.

• Bedroom example: Four walls at 12 ft × 9 ft (432 sq ft gross), one 3 ft × 5 ft window and one 3 ft × 7 ft door subtracted (36 sq ft of openings), two coats, plus a 12 ft × 12 ft ceiling. Net wall area is 396 sq ft; at two coats and 400 sq ft per gallon, that comes to about 2 gallons of wall paint, with the 144 sq ft ceiling needing about 3 quarts separately.
• Living room with gable: Two standard walls and two walls with a peak, the peak rise entered to capture the triangular area accurately, plus larger window openings and crown molding.
• Exterior accent wall: One large wall in Exterior mode, with two windows subtracted, one coat for primer and one for finish, and total gallons rounded up for a small buffer.

The surface area line confirms the inputs, and wall and ceiling paint are reported separately. Results round to the nearest quart in Imperial and to two decimal places in Metric, so the purchase covers the project without frequent return trips. The ceiling line lets ceiling paint be bought separately from wall paint when the two use different finishes.

Yes. Higher-quality paints and certain sheens cover differently. The provided rates work as a baseline, with a safety margin added for textured or porous surfaces.

Yes. The coat count should rise when a plan includes primer or a specialty undercoat, which keeps totals realistic for new drywall or a drastic color change.

Irregular ceilings break into rectangles that can be measured and entered as separate ceilings. Complex shapes approximate well as several rectangles added together for total area.