Interior Paint Calculator

Whether you’re giving your living room a fresh look or repainting your entire home, estimating the right amount of paint is crucial. Buying too much results in waste and unnecessary expense; buying too little interrupts your workflow and requires extra trips to the store. To help you plan your painting projects efficiently, we’ve built a free Interior Paint Calculator right here on our website.

This simple, interactive tool makes it easy to determine exactly how much paint you’ll need based on your room’s dimensions, the number of coats you plan to apply, and adjustments for doors and windows. In just seconds, you’ll have a professional estimate without any complex math.

How to Use the Interior Paint Calculator – Step-by-Step

Using the calculator is quick and beginner-friendly. Here’s how to get an accurate estimate:

Step 1: Enter Room Dimensions

Start by measuring your room and entering the values in feet:

  • Room Length (ft): The longer side of the room.
  • Room Width (ft): The shorter side of the room.
  • Room Height (ft): Floor to ceiling.

Step 2: Account for Doors and Windows

Input the number of:

  • Doors (each door subtracts ~20 sq ft from wall area).
  • Windows (each window subtracts ~15 sq ft from wall area).

This ensures your estimate reflects the actual paintable surface.

Step 3: Select Number of Coats

How many coats of paint will you apply? One is standard, but choose more if you’re painting over dark colors or using a lighter paint.

Step 4: Specify Paint Coverage

Most paint covers 350 sq ft per gallon, which is the default. You can adjust this value based on the specifications provided on your paint can or manufacturer’s website.

Step 5: Click “Calculate”

Click the Calculate button and the tool will instantly display:

  • Total Paintable Area in square feet.
  • Gallons Required (rounded up for convenience).

Click Reset to start over or calculate a new room.

Example: Calculating Paint for a Standard Bedroom

Let’s walk through a real-world example using the calculator.

Room Specifications:

  • Length: 12 ft
  • Width: 10 ft
  • Height: 8 ft
  • Doors: 1
  • Windows: 2
  • Coats: 2
  • Coverage: 350 sq ft per gallon

Step-by-Step:

  1. Wall Area: 2 x 8 x (12 + 10) = 352 sq ft
  2. Subtract doors/windows: 352 - (1x20 + 2x15) = 302 sq ft
  3. Apply coats: 302 x 2 = 604 sq ft
  4. Calculate gallons: 604 / 350 = 1.73 gallons

Result: You need 2 gallons of paint for this project.

Why Use a Paint Calculator?

While you could estimate by guesswork or vague rules of thumb, our paint calculator offers the following advantages:

  • ✅ Accuracy: Takes all key variables into account.
  • ✅ Time-Saving: Instant results mean faster planning.
  • ✅ Money-Saving: Avoid buying too much or too little.
  • ✅ Project Clarity: Know exactly what to buy before heading to the store.

When to Use This Tool

This calculator is ideal for:

  • Homeowners planning DIY paint jobs.
  • Contractors estimating supplies for client projects.
  • Interior designers drafting preliminary budgets.
  • Property managers overseeing maintenance and renovations.
  • Renters wanting to spruce up temporary spaces.

It’s especially helpful when dealing with multiple rooms—you can run the calculation separately for each one and tally the totals.

Pro Tips for Accurate Paint Estimation

  • Measure carefully: Use a tape measure and round up to the nearest half-foot.
  • Account for texture: Rough walls (like stucco) require more paint.
  • Check manufacturer specs: Coverage varies by brand and type (primer, matte, semi-gloss).
  • Always round up: Paint cans aren’t sold in fractions—round up to the next full gallon.

FAQs – Interior Paint Calculator

Here are some of the most common questions about our paint calculator tool:

1. How accurate is this tool?

Very accurate for general interior projects. It factors in wall area, door/window deductions, coats, and paint coverage.

2. Can I use this for ceilings or trim?

No, this tool is designed for walls only. Ceilings and trim need separate calculations.

3. What if my room has more than four walls?

You can break it into sections or manually total up all wall areas and use that number.

4. Why subtract door and window area?

They don’t require paint—subtracting them gives you a more accurate paintable surface.

5. Is the coverage value adjustable?

Yes! You can enter any number to match your specific paint brand’s coverage rate.

6. Should I include closet areas?

If you’re painting inside closets, treat them as separate mini-rooms and calculate accordingly.

7. Does wall texture affect the result?

Yes. Rough surfaces like stucco or brick absorb more paint. Add 10–20% to your total.

8. What if I’m using primer and paint separately?

Run the calculation twice: once for primer, once for paint.

9. Can I use this tool for exterior walls?

No. Exterior paint requires different considerations—use an exterior-specific calculator.

10. Do I need to account for multiple rooms?

Yes. Run the calculator separately for each room, then add up total gallons.

11. What’s the average room size?

A typical bedroom is about 12×10 ft with 8-ft ceilings.

12. How many coats should I use?

One coat for same-color refresh, two for color changes or covering dark tones.

13. Can I save my results?

Not directly, but you can take a screenshot or note them down.

14. Is it okay to buy a little extra paint?

Yes, having 5–10% extra helps with touch-ups or miscalculations.

15. What’s the difference between flat, eggshell, and satin paint?

Only coverage slightly changes. Use manufacturer specs for best accuracy.

16. What if my room has built-in furniture?

If furniture covers wall sections (like large wardrobes), you can subtract that area manually.

17. Does paint type matter?

Yes—some specialty paints (like stain-blocking or waterproof types) have lower coverage.

18. How do I measure odd-shaped rooms?

Break them into rectangles and add up the areas.

19. What’s the best time to paint indoors?

When temperatures are stable (above 50°F) and ventilation is good.

20. How long does a gallon of paint last?

An unopened can typically lasts 2–5 years if stored properly.

Final Thoughts

Estimating paint doesn’t have to be a hassle. Our Interior Paint Calculator simplifies the process, so you can focus on choosing colors and getting the job done. With just a few measurements and clicks, you’ll get a reliable paint estimate that saves you time, money, and stress.