What Is the Paint Calculator?
The Paint Calculator is a free online tool designed for contractors and DIY builders who need quick, accurate calculations in the construction and building space. By entering your input method, room length, room width, you get instant results including gallons needed, estimated cost. No formulas to memorize, no spreadsheets to build — just enter your numbers and get the answer in seconds. Whether you're a beginner or experienced professional, this calculator saves you time and eliminates guesswork.
Why This Calculation Matters
Getting gallons needed right can make the difference between success and costly mistakes. In construction and building, small errors compound quickly. Manual calculations are error-prone and time-consuming, especially under pressure. This calculator applies proven formulas used by contractors and DIY builders worldwide, giving you confidence that your numbers are correct. Use it to plan your projects with precision and avoid common pitfalls that trip up beginners.
When Should You Use This Calculator?
This tool is most useful when you know your input method and need to find the right gallons needed. It's also great for quick estimates before committing to a decision, and to double-check manual calculations or professional quotes, and when comparing different scenarios side by side. Bookmark this page and come back whenever you need a fast, reliable answer — the calculator is always free and requires no signup.
Paint Calculator
Paint Coverage Quick Reference
Gallons needed for 2 coats at 350 sq ft/gallon coverage.
| Room Size | Wall Area (sq ft) | After Openings | Gallons (2 coats) | With Ceiling |
|---|---|---|---|---|
| 10 x 10, 8' walls | 320 | 284 | 2 | 3 |
| 10 x 12, 8' walls | 352 | 316 | 2 | 3 |
| 12 x 12, 8' walls | 384 | 348 | 2 | 3 |
| 12 x 16, 8' walls | 448 | 412 | 3 | 4 |
| 14 x 16, 8' walls | 480 | 444 | 3 | 4 |
| 16 x 20, 8' walls | 576 | 540 | 4 | 5 |
| 20 x 20, 8' walls | 640 | 604 | 4 | 6 |
How to Use This Calculator
- Enter Your Input Method: Start by entering your input method — this is the primary input for the calculation.
- Fill In Additional Details: Complete the remaining fields: room length, room width, wall height, total wall area, number of doors, number of windows, number of coats, paint coverage, include ceiling?, price per gallon. Each value refines the calculation for greater accuracy.
- Click Calculate: Hit the Calculate button to run the numbers. Results appear instantly below.
- Review Your Results: Check your gallons needed, estimated cost. Use these figures to inform your next decision or compare against alternative scenarios.
How It Works
Calculating paint quantity starts with finding your total paintable wall area, subtracting openings, then dividing by the paint's coverage rate per gallon.
The basic rule:
- Wall area = perimeter (2 × length + 2 × width) × height, minus doors (21 sq ft each) and windows (15 sq ft each)
- One gallon of interior paint covers 350-400 sq ft on smooth walls; textured walls may drop to 250-300 sq ft
- Always plan for 2 coats — the first coat seals the surface and the second provides full, even coverage
This calculator rounds up to the nearest gallon. If you are close to a whole number, consider buying quarts to supplement. Most paint stores will tint quarts to match your gallon color. Keep leftover paint for future touch-ups.
Tips & Considerations
- Double-check your input method before calculating — even small input errors can significantly change your results.
- Run the calculator with different values to compare scenarios and find the optimal approach for your situation.
- Pay attention to both gallons needed and estimated cost — they work together to give you the full picture.
- Bookmark this page for quick access next time you need to plan your projects.
- If you're unsure about your price per gallon, start with a conservative estimate and adjust from there.
Frequently Asked Questions
How many square feet does a gallon of paint cover?
A gallon of interior paint covers 350-400 square feet on smooth, primed walls. Textured or porous surfaces reduce coverage to 250-300 square feet. Exterior paint typically covers 250-350 square feet per gallon depending on the surface texture.
Do I really need 2 coats of paint?
Yes, two coats are recommended for most projects. The first coat seals the surface and provides a base, while the second coat ensures uniform color and full coverage. You might get away with one coat if you are painting the exact same color over a well-prepared surface.
How much paint do I need for a 12x12 room?
A 12x12 room with 8-foot ceilings has about 384 square feet of wall area. After subtracting a door and two windows, that is roughly 333 square feet. At 350 sq ft/gallon with 2 coats, you need about 2 gallons for the walls, plus 1 gallon for the ceiling if painting it.
Should I buy paint in gallons or 5-gallon buckets?
If you need 3 or more gallons of the same color, a 5-gallon bucket is usually cheaper per gallon and ensures color consistency. For smaller jobs, individual gallons are fine. Always buy all your paint at once — even the same color code can vary slightly between batches.
How do I estimate paint for trim and baseboards?
Trim paint (doors, baseboards, crown molding) typically requires 1 quart per standard door (both sides plus frame) and about 1 quart per 100-150 linear feet of trim. A typical room with one door and standard baseboards needs about 1-2 quarts of trim paint.
What is the difference between flat, eggshell, and satin paint?
Flat/matte paint hides imperfections but is hard to clean — best for ceilings and low-traffic areas. Eggshell has a slight sheen and is washable — ideal for living rooms and bedrooms. Satin is more durable and moisture-resistant — best for kitchens, bathrooms, and trim.