Paint Calculator
Paint calculator
Estimate wall and ceiling paint, subtract openings, and plan what to buy.
9 ft walls, 1 door, 2 windows, walls only
Typical repaint on smooth drywall
Live purchase estimate
2 gal + 2 qt
Exact paint 2.29 gal
Openings to subtract
Door 21 ft² · Window 15 ft²
Low-waste US container mix
2 gal + 2 qt
Exact paint: 2.29 gal
Template: Primary bedroom (14x12 ft) • Coverage preset: Interior latex (smooth wall)
Paintable area
417 ft²
With coats
834 ft²
With allowance
917.4 ft²
Openings
−51 ft²
Primer
Not included
Area and purchase steps
- Walls 468 ft²; ceiling Not included; openings −51 ft².
- Template: Primary bedroom (14x12 ft). Coverage preset: Interior latex (smooth wall).
- 417 ft² × 2 coats = 834 ft².
- 10% extra allowance gives 917.4 ft².
- Divide by label coverage 400 ft²/gal = 2.29 gal.
- 2 gal + 2 qt buys 2.5 gal with 0.21 gal beyond the estimate.
Formula
Net area = Walls + Ceiling - Openings Coverage area = Net area x Coats x (1 + Allowance) Paint = Coverage area / Label coverage G = \frac{A_t}{R} - Compute four-wall area from room perimeter and height, then optionally add the ceiling.
- Subtract standard door/window allowances and any extra excluded area.
- Multiply net paintable area by coats and the selected extra allowance.
- Divide by the coverage printed on the selected paint; primer is estimated separately with its own coverage.
Example
Worked example: 14x12 room, 9 ft walls, one door, two windows
- 1 Wall area = 2(14+12)x9 = 468 ft².
- 2 Openings = 1x21 + 2x15 = 51 ft², so net area = 417 ft².
- 3 Two coats with 10% extra = 417x2x1.10 = 917.4 ft² of coverage.
- 4 At 400 ft² per gallon, exact paint = 917.4/400 = 2.29 gallons.
The low-waste US container mix is 2 one-gallon cans plus 2 quarts (2.5 gallons total).
How
- Choose Room for dimensions or Known area when you already measured the net surface.
- In Room mode, pick a room template to preload typical dimensions/openings or keep Custom for manual entry.
- Select imperial or metric units, then enter dimensions or paintable area.
- For a room, choose whether to include the ceiling and enter door, window, and extra exclusions.
- Choose a coverage preset (or Custom), then set coats, extra allowance, and optional primer.
- Review exact gallons/liters, the area breakdown, and the suggested purchase quantity.
Avoid
- Using a generic coverage rate instead of the value printed on the selected product.
- Forgetting that coats multiply the full net paintable area.
- Subtracting doors and windows twice when entering an already-net Known area.
- Treating primer coverage as identical to finish-paint coverage.
- Rounding exact gallons without checking the package sizes sold locally.
FAQ
Does this include doors and windows deduction?
Yes. Room mode subtracts 21 ft² per door and 15 ft² per window, plus any extra excluded area. Use Known area when you have exact measured deductions.
What coverage rate should I enter?
Start with a coverage preset close to your surface and product class, then replace it with the exact paint or primer label value when available. Texture, porosity, and application method can change real coverage.
Can I use metric dimensions?
Yes. Metric mode accepts meters, square meters, and square meters per liter while preserving the same physical project when units change.
How does the US container recommendation work?
It rounds the exact requirement up to the next quart, then expresses it as 5-gallon pails, 1-gallon cans, and quarts to minimize volume above the estimate. Package sizes and pricing vary by market.
Does the paint estimate include primer?
Primer is optional and calculated separately as one coat using its own label coverage. The selected extra allowance applies to both paint and primer.
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