Paint Coverage Calculator Formula
Understand the math behind the paint coverage calculator. Each variable explained with a worked example.
Formulas Used
Gallons Needed
gallons_needed = ceil(paintable_area / 350)Paintable Wall Area
total_wall_sqft = wall_area - deductionsTotal Coverage (with coats)
total_coverage_needed = paintable_areaVariables
| Variable | Description | Default |
|---|---|---|
room_length_ft | Room Length(ft) | 15 |
room_width_ft | Room Width(ft) | 12 |
ceiling_height_ft | Ceiling Height(ft) | 8 |
num_doors | Number of Doors | 2 |
num_windows | Number of Windows | 3 |
coats | Number of Coats | 2 |
wall_area | Derived value= 2 * (room_length_ft + room_width_ft) * ceiling_height_ft | calculated |
deductions | Derived value= num_doors * 21 + num_windows * 15 | calculated |
paintable_area | Derived value= (wall_area - deductions) * coats | calculated |
How It Works
Calculating Paint Coverage
To paint a room, calculate the total wall area minus doors and windows, then divide by the paint coverage rate.
Formula
Wall Area = 2 x (Length + Width) x Height
Paintable Area = Wall Area - (Doors x 21 sq ft) - (Windows x 15 sq ft)
Gallons = (Paintable Area x Coats) / 350 sq ft per gallon
Most interior latex paints cover 350-400 sq ft per gallon on smooth surfaces. Textured walls or dark-to-light color changes may need additional paint.
Worked Example
A 15 x 12 foot room with 8-foot ceilings, 2 doors, 3 windows, 2 coats.
room_length_ft = 15room_width_ft = 12ceiling_height_ft = 8num_doors = 2num_windows = 3coats = 2
- 01Wall area = 2 x (15 + 12) x 8 = 432 sq ft
- 02Deductions = 2 x 21 + 3 x 15 = 42 + 45 = 87 sq ft
- 03Paintable area = 432 - 87 = 345 sq ft
- 04With 2 coats = 345 x 2 = 690 sq ft total
- 05Gallons = ceil(690 / 350) = 2 gallons
Ready to run the numbers?
Open Paint Coverage Calculator