Free tool
Paint Calculator
Calculate how many gallons of paint a room needs and what the paint will cost.
Enter a room's dimensions and number of coats to find out how much paint you need and what it costs. The calculator figures wall area (minus a typical allowance for doors and windows), optionally adds the ceiling, and rounds up to whole gallons. Remember: on a hired job, labor is usually the bigger cost.
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- Updates instantly
- Built for service businesses
- Shareable link to your scenario
Quick startPick your industry to load real-world numbers
Your inputs
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Quality interior paint runs about $30 to $60 per gallon.
Paint Calculator
Calculated November 10, 2026
- Room length (ft)
- 12
- Room width (ft)
- 12
- Ceiling height (ft)
- 9
- Number of coats
- 2
- Also paint the ceiling
- No
- Paint price per gallon
- $40
Your results
Gallons of paint needed
3
Rounded up to whole gallons, for the coats selected
Where this number comes from
Painting a single interior room typically costs $300 to $800 hired out, far more than the paint itself, because prep and labor dominate. Quality interior paint runs about $30 to $60 per gallon.
Smarfle painting-cost pricing guide
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Smarfle builds branded painting estimates (prep, labor, and materials separated), sends them for online approval and a deposit, and turns them into scheduled jobs and invoices.
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How this calculation works
Paint quantity comes from area and coats: 1. Wall area = 2 x (length + width) x ceiling height, minus about 10% for an average set of doors and windows. 2. Ceiling (optional) = length x width. 3. Coverage: one gallon of interior paint covers roughly 350 sq ft per coat. 4. Gallons = total area x coats / 350, rounded up to whole gallons. For a hired job, paint is only part of the cost. Prep and labor usually dominate, which is why a painted room costs far more than the paint alone.
Real scenarios
Find the persona closest to yours, then click to load those numbers into the calculator.
DIY homeowner
Repainting a 12 x 12 bedroom, two coats.
About 3 gallons and ~$120 in paint. Buy one extra quart for touch-ups.
Large room + ceiling
16 x 20 living room, walls and ceiling.
Including the ceiling adds meaningfully to the gallons. The calculator splits the area for you.
Painter estimating materials
Pricing a job.
Use the gallon count to lock material cost, then add prep and labor (the bigger numbers) in your estimate.
Smarfle
Run this in your business, not just in a calculator
These Smarfle features close the loop on what this tool surfaces. Built for local service businesses, used by HVAC, plumbing, electrical, cleaning, lawn care, and 40+ other trades.
Estimates
Build a painting estimate that separates prep, labor, and materials so customers see the value.
Learn moreInvoicing
Turn the accepted estimate into an invoice with online payment.
Learn morePayment Links
Collect a deposit before you buy the paint, and the balance on completion.
Learn moreFrequently asked questions
How much paint do I need for a room?
How many square feet does a gallon of paint cover?
Do I need two coats?
Why does a painted room cost so much more than the paint?
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