# Paint Quantity Calculator

> Calculate gallons of paint needed for a room, accounting for windows, doors, and multiple coats

**Category:** Construction
**Keywords:** paint, gallons, room, wall, coverage, coats, interior, painting, square feet, windows, doors, construction, home improvement
**URL:** https://complete.tools/paint-quantity-calculator

## How it calculates

The calculator uses a straightforward set of formulas based on room geometry:

**Total Wall Area:**
```
Total Wall Area = 2 x (Length + Width) x Height
```

**Deductions for Openings:**
```
Window Area = Number of Windows x Window Width x Window Height
Door Area = Number of Doors x Door Width x Door Height
Total Deductions = Window Area + Door Area
```

**Net Paintable Area and Gallons:**
```
Net Paintable Area = Total Wall Area - Total Deductions
Total Coverage Needed = Net Paintable Area x Number of Coats
Gallons Needed = Total Coverage Needed / Coverage Rate per Gallon
Gallons to Buy = Round up to nearest whole gallon
```

The default coverage rate is 350 square feet per gallon, which is typical for standard latex interior paint on smooth drywall. You can adjust this value for different paint types or surface textures. The result is always rounded up to the next whole gallon because paint is sold in full gallons.

## Standard sizes used

When custom sizes are not enabled, the calculator uses these standard dimensions:

- **Standard window**: 3 feet wide by 4 feet tall (12 square feet each)
- **Standard door**: 3 feet wide by 7 feet tall (21 square feet each)

These represent common residential window and door sizes in North America. If your windows or doors are a different size, enable custom sizing to enter the exact dimensions. For rooms with mixed window sizes, use an average or calculate each wall separately.

## Coverage rates by paint type

Different paints cover different amounts of surface area per gallon:

- **Standard latex (flat/matte)**: 350-400 sq ft per gallon on smooth surfaces
- **Eggshell or satin finish**: 300-350 sq ft per gallon
- **Semi-gloss or gloss**: 300-350 sq ft per gallon
- **Primer**: 200-300 sq ft per gallon, depending on surface porosity
- **Textured paint**: 150-200 sq ft per gallon

Porous or rough surfaces like bare wood, new drywall, or textured walls absorb more paint and reduce effective coverage. Previously painted smooth walls typically achieve the best coverage rates. Always check the paint can label for the manufacturer's recommended coverage rate.

## FAQs

**Q:** How many coats of paint do I need? 

**A:** Most interior painting projects require 2 coats for even, consistent coverage. You may need only 1 coat if you are repainting with the same or a very similar color. Use 3 coats when painting over a dramatically different color (such as dark to light) or when using a lighter-colored paint over a dark base.


**Q:** Does the calculator include the ceiling? 

**A:** No, this calculator only estimates paint for the four walls of a room. Ceilings are typically painted with a separate ceiling paint. To calculate ceiling paint, multiply the room length by the room width and divide by your paint coverage rate.


**Q:** Should I subtract for baseboards and trim? 

**A:** The calculator does not subtract for baseboards or trim since these small areas are typically negligible and the extra paint provides a useful buffer for touch-ups. If you are painting trim a different color, calculate trim paint separately.


**Q:** What if my room is not rectangular? 

**A:** For L-shaped or irregular rooms, break the space into rectangular sections and calculate each section separately. Add the results together for your total paint estimate. Alternatively, measure the perimeter of the room directly and multiply by the wall height for total wall area.


**Q:** How much extra paint should I buy for touch-ups? 

**A:** The calculator rounds up to the nearest gallon, which usually provides enough extra for minor touch-ups. For ongoing maintenance, keep at least a quart stored for future scuffs and marks. Most latex paint stays usable for 2-10 years when stored properly in a sealed container at room temperature.


**Q:** Why does the coverage rate matter? 

**A:** The coverage rate determines how many square feet one gallon of paint can cover. Using the wrong rate leads to buying too much or too little paint. Check your specific paint product label for the recommended spread rate. Smooth walls with a good primer coat achieve higher coverage than rough or porous surfaces.

## How to use

1. Enter your room dimensions: length, width, and wall height in feet
2. Specify the number of windows and doors in the room
3. Toggle custom sizes if your windows or doors differ from the standard 3x4 ft window and 3x7 ft door
4. Set the number of coats (2 coats is recommended for most projects)
5. Adjust the coverage rate if you are using a specialty paint (default is 350 sq ft per gallon)
6. View the total gallons needed, along with a detailed breakdown of wall area, deductions, and net paintable area
7. Purchase the recommended number of whole gallons at your local paint or hardware store

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*Generated from [complete.tools/paint-quantity-calculator](https://complete.tools/paint-quantity-calculator)*