Paint Calculator
Estimate how many gallons of paint are needed for walls and ceilings based on room dimensions and coverage rate.
This free online paint calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.
Minimum: 0
Perimeter of the room
Minimum: 0
Floor to ceiling height
Total area of doors and windows
Typically 2 coats for good coverage
Typical paint covers 300-400 sq ft per gallon
Results
Paintable Area
376 sq ft
Gallons Needed
3
How to Use This Calculator
Enter your input values
Fill in all required input fields for the Paint Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.
Review your inputs
Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.
Read the results
The Paint Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.
Explore parameter sensitivity
Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.
Formula Reference
Paint Calculator Formula
See calculator inputs for the governing equation
Variables: All variables and their units are labeled in the calculator interface above. Input fields accept values in multiple unit systems — select your preferred unit from the dropdown next to each field.
When to Use This Calculator
- •Use the Paint Calculator when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
- •Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
- •Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
- •Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.
About This Calculator
The Paint Calculator is a free, browser-based calculation tool for engineers, students, and technical professionals. Estimate how many gallons of paint are needed for walls and ceilings based on room dimensions and coverage rate. It implements standard formulas and supports both metric (SI) and imperial unit systems with automatic unit conversion. All calculations are performed instantly in your browser with no data sent to a server. Use this calculator as a quick reference and sanity-check tool during design, analysis, and learning. Always verify results against primary engineering references and applicable standards for any safety-critical application.
About Paint Calculator
Nothing transforms a room faster than a fresh coat of paint, but buying too much wastes money and buying too little means an extra trip to the store -- where the new batch might not match perfectly. This calculator takes your room dimensions, subtracts window and door openings, multiplies by the number of coats, and divides by the paint coverage rate to give you the number of gallons needed. Most interior latex paints cover 300 to 400 square feet per gallon on smooth surfaces, with textured walls requiring more paint. Two coats are standard for a quality finish, especially when changing colors. Using this calculator ensures you purchase just the right amount for a professional-looking result.
The Math Behind It
Formula Reference
Paint Gallons
Gallons = (Paintable Area x Coats) / Coverage Rate
Variables: Paintable area = Wall area - Openings. Coverage in sq ft per gallon.
Worked Examples
Example 1: Living room 14x18 ft, 9 ft ceilings, 2 coats
Perimeter = 2(14+18) = 64 ft, Height = 9 ft, Openings = 50 sq ft, Coats = 2, Coverage = 350 sq ft/gal
You need 3 gallons of paint.
Common Mistakes & Tips
- !Forgetting to multiply by the number of coats.
- !Using the coverage rate for smooth surfaces on textured walls.
- !Not accounting for primer as a separate purchase when painting over dark colors.
- !Overlooking ceiling area when planning a complete room repaint.
Related Concepts
Used in These Calculators
Calculators that build on or apply the concepts from this page:
Frequently Asked Questions
How much area does one gallon of paint cover?
Most interior latex paints cover 350 to 400 square feet per gallon on smooth surfaces. Textured surfaces, porous surfaces, and dark-to-light color changes reduce coverage significantly.
Do I need primer?
Primer is recommended when painting new drywall, covering stains, changing from dark to light colors, or switching between paint types (e.g., oil-based to latex). Self-priming paints can sometimes eliminate this step for routine repaints.