MaterialMeasure

Interior

Paint Calculator

Enter room dimensions, openings, coats, coverage, and waste allowance to estimate gallons or quarts of paint.

Planning estimate

This calculator provides a planning estimate only. Material coverage, compaction, waste, surface conditions, product yield, and installation methods can change the final quantity needed. Always check the product label and local supplier guidance before purchasing materials.

How To Use This Calculator

  1. Step 1 Enter room length, width, and wall height to calculate wall area before openings.
  2. Step 2 Use the door and window fields to subtract areas that will not be painted. Set them to zero if you prefer a conservative rounded estimate.
  3. Step 3 Change coverage per gallon to match the paint label, primer plan, wall texture, and number of coats.

What The Result Means

The paint result shows wall area, paintable area, gallons, rounded gallons, and rounded quarts. The rounded quantity is the practical shopping number, while the exact gallon estimate helps compare one-coat and two-coat plans.

If you need floor area for tile or flooring, use the square footage calculator instead of the paint calculator.

Before You Buy

  • Check whether primer is needed for stains, raw drywall, patched areas, or major color changes.
  • Read the product label for coverage per gallon and recommended coats.
  • Buy enough paint from the same tint batch when color consistency matters.
  • Keep a small amount for touch-ups after trim, furniture, and outlet covers go back in place.

Accuracy Notes

  • Textured walls, porous surfaces, and dark-to-light changes can lower coverage.
  • Sprayers and rollers can have different transfer loss.
  • Openings are estimated unless you measure each door and window.

Formula

Wall area = 2 × (length + width) × wall_height

Paintable area = wall_area - door_area - window_area

Gallons = paintable_area × coats / coverage_per_gallon

Adjusted gallons = gallons × (1 + waste_factor)

Example Project

A 12 ft by 10 ft room with 8 ft walls has 352 sq ft of wall area before subtracting doors and windows.

Waste Factor

Use 5-10% for touch-ups, roller loss, and surface variation. Use more when changing color dramatically or painting textured walls.

Unit Notes

Coverage is entered as square feet per gallon because product labels vary by paint line and surface.

Common Mistakes

  • Forgetting the second coat.
  • Assuming every paint covers the same area.
  • Subtracting openings twice or using unrealistic door/window areas.

FAQ

How much does one gallon of paint cover?

Many labels are around 300-400 square feet per gallon, but coverage depends on paint, primer, texture, and color change.

Should I subtract doors and windows?

Yes for a closer estimate, especially in rooms with many openings. For small projects, rounding up may already cover the difference.

Related Calculators

Measurement Square Footage Calculator Calculate square feet, square yards, and square meters for rectangles, triangles, circles, and L-shaped rooms. Open calculator Flooring Tile Calculator Estimate tile count, floor area, waste-adjusted quantity, and box count for bathrooms, kitchens, and small floors. Open calculator Yard Materials Mulch Calculator Estimate mulch cubic feet, cubic yards, and bag counts for flower beds, tree rings, and garden areas. Open calculator