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Paint Calculator

Room length

Room width

Wall height

Coats

Paint needed

2.4

1-gal cans to buy: 3
Paintable wall area: 414

HI data benchmark

The estimate above is personalized to your inputs. These are HI's independent market reference figures from its data layer — each shown with its source and confidence.

Where	Measure	Value	Confidence
US national · Interior painting (home project)	Low (USD per room repaint)	$200	Modeled estimate
US national · Interior painting (home project)	Median (USD per room repaint)	$450	Modeled estimate
US national · Interior painting (home project)	High (USD per room repaint)	$900	Modeled estimate

Methodology: US local service / home-project cost (v1)

Sources: U.S. BLS — Occupational Employment & Wage Statistics HI Internal Cost Estimation Model Industry Home-Project Pricing References (uncleared)

Dataset: US Local Service & Home-Project Cost — see data products

v0 values are modeled estimates pending verified collection. Educational use, not financial advice.

Estimate how many gallons of paint you need from a room's dimensions, number of coats, and openings.

By Jordan P. · Reviewed by Cara M., Licensed Contractor · Updated 2026-06-03

Quick answer

Calculate wall area as 2 × (length + width) × height, subtract about 18 ft² per door or window, multiply by the number of coats, then divide by the paint’s coverage (about 350 ft² per gallon). Round up to whole cans.

How to use this calculator

Measure the room's length, width, and ceiling height in feet.
Set the number of coats — two is standard over a new or darker color.
Under Advanced, subtract doors and windows and adjust gallon coverage if your paint differs.
Round up to whole cans when buying so you have enough for touch-ups.

Formula

Gallons = [ (2(L + W) × H − openings) × coats ] ÷ coverage

L, W — room length and width
H — wall height
coverage — ft² one gallon covers (≈350)

Worked example

A 14 × 12 room with 9-ft walls has about 468 ft² of wall. Removing three openings (~54 ft²) and applying two coats needs roughly 828 ft² of coverage — about 2.4 gallons, so buy 3 one-gallon cans.

Frequently asked questions

How much wall does a gallon of paint cover?

A gallon typically covers 350–400 ft² in one coat on a smooth, primed surface. Rough or unprimed walls absorb more, so coverage drops.

How many coats do I need?

Two coats is standard for even color and durability. One coat may work when repainting a similar color over a good primer.

Do I subtract doors and windows?

Yes — subtracting openings avoids over-buying. We use about 18 ft² per door or window as an average; adjust the count for large windows.

Does the ceiling need separate paint?

This estimate covers walls only. For the ceiling, calculate length × width as a separate area and add it.

Should I buy extra?

Round up to whole cans and keep some leftover for touch-ups. Buying all your paint at once also keeps the color batch consistent.

What about primer?

Bare drywall, patches, or big color changes need primer, which is a separate coat with similar coverage to paint.

Related calculators

Jordan P. · Author

Reviewed by Cara M., Licensed Contractor · Updated 2026-06-03

Sources

EPA — Lead-safe painting practices — Safe prep guidance.
Manufacturer coverage specs (typical) — 350–400 ft²/gal basis.

Methodology · Report an error

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View answer.json (AI feed)

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  "question": "How much paint do I need for a room?",
  "answer": "Calculate wall area as 2 × (length + width) × height, subtract about 18 ft² per door or window, multiply by the number of coats, then divide by the paint’s coverage (about 350 ft² per gallon). Round up to whole cans.",
  "formula": "Gallons = [ (2(L + W) × H − openings) × coats ] ÷ coverage",
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