Paint Calculator

Estimate how much paint you need in gallons and quarts based on wall area, room size, coats, coverage rate, and a waste buffer.

Enter Your Project Size


Use room dimensions if you know the room size. Use known area if you already measured the paintable square feet.


Measure one long wall.


Measure one short wall.


Most standard rooms are around 8 feet high.


Use 1 unless painting multiple similar rooms.


Ceiling area is length × width.


Subtracts about 21 sq ft per standard door.


Subtracts about 15 sq ft per average window.


Use 2 coats for many repainting projects.


Many paints list about 300–400 sq ft per gallon. Check the label.


Adds extra for texture, touch-ups, roller loss, and mistakes.


Optional. Enter 0 if you do not want a cost estimate.


Your Results

Paint needed

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Enter values and calculate.

Suggested purchase

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Rounded up for buying paint.

Paintable area

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Before coats and buffer.

Estimated cost

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Uses your price per gallon.

This calculator gives a planning estimate only. Real paint needs can vary because of wall texture, color change, primer, surface condition, paint quality, roller type, and product coverage.

How to Use This Paint Calculator

Enter the room dimensions or the known paintable area, then choose the number of coats and paint coverage rate. The calculator estimates gallons, suggested purchase amount, paintable area, and optional cost.

For a room calculation, doors and windows are subtracted using rough average areas. If you need a more accurate estimate, measure the actual openings and use the known-area option.

Formula Used

Wall area = 2 × height × (length + width)
Ceiling area = length × width
Paintable area = wall area + ceiling area − doors − windows
Total coated area = paintable area × number of coats
Adjusted area = total coated area × (1 + buffer %)
Gallons needed = adjusted area ÷ paint coverage per gallon

Example Calculation

A 12 ft × 10 ft room with 8 ft walls has:

2 × 8 × (12 + 10) = 352 square feet of wall area

After subtracting one door and two windows, the paintable wall area is about 301 square feet. With two coats and a 10% buffer, that becomes about 662 square feet of coverage needed.

If the paint covers 350 square feet per gallon, the estimate is about 1.9 gallons, so buying 2 gallons is a practical starting point.

Common Paint Estimating Mistakes

  • Forgetting to multiply by the number of coats.
  • Assuming every paint covers exactly the same area.
  • Ignoring wall texture, repairs, primer, and strong color changes.
  • Buying exactly the calculated amount with no touch-up buffer.
  • Counting ceiling paint and wall paint as the same paint when different products are used.
  • Subtracting doors and windows too aggressively, then running short.

Important Planning Note

Use this calculator as a planning tool only. Check the actual paint label for coverage, drying time, coat recommendations, primer requirements, and surface preparation instructions.

For damaged drywall, stains, smoke residue, glossy surfaces, bare wood, masonry, or major color changes, the real amount of paint or primer needed may be higher than the calculator result.