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How Much Paint Do I Need?

One gallon of paint covers 350–400 square feet on smooth walls, but textured surfaces like orange peel or knockdown need more. Enter your room dimensions below to get an exact estimate with 10% extra for waste.

Perfect for DIY homeowners, painting contractors, property managers, and real estate flippers.

This calculator is for you if...

First time painting a roomTired of making multiple store tripsHave textured wallsDoing a color change

Why Most People Buy the Wrong Amount of Paint

They Use "One Gallon = 400 sq ft"

That number is for smooth, sealed surfaces with perfect application. Real walls — especially textured ones — absorb significantly more paint.

They Forget About Surface Texture

Knockdown texture has 30-40% more surface area than flat walls. Popcorn ceilings can use twice as much paint. This calculator adjusts for your actual texture.

They Don't Account for Waste

Paint left in the roller, drips, absorption, touch-ups — you lose about 10% of every gallon. Buy exactly what the can says and you'll run short.

They Underestimate Color Changes

Going from dark to light? Two coats won't cut it. You need three coats minimum to prevent the old color from bleeding through.

Quick Reference: Coverage by Texture

Smooth Drywall: 350-400 sq ft/gallon

Orange Peel: 300-350 sq ft/gallon

Knockdown: 250-300 sq ft/gallon

Popcorn/Heavy: 200-250 sq ft/gallon

Stucco/Brick: 150-200 sq ft/gallon

PAINT CALCULATOR

How Much Paint Do I Need?

Get an accurate estimate for primer and paint based on your room dimensions and surface texture.

Room Details

Coverage: 375 sq ft/gal paint, 350 sq ft/gal primer

$

Enter your paint price to see estimated total cost

Your Paint Estimate

Primer

1.5

gal

Paint

2.5

gal (2x)

Total

4.0

gal

Est. Cost

—

enter price

Shopping List

Buy 2 gallons of primer

Buy 3 gallons of paint

Show the Math

Net Coverage Area: 400 + 0 - (1 doors × 20 + 2 windows × 17.5) = 345 sq ft

Primer: (345 ÷ 350) × 1.1 waste factor = 1.5 gal

Paint: (345 ÷ 375) × 2 coats × 1.1 waste factor = 2.5 gal

Why add 10% waste? Paint is lost to roller nap, brush absorption, drips, touch-ups, and uneven surfaces. Planning for 10% extra prevents mid-project store runs.

Tool powered by Blessed Arc Media - Web Design for Home Service Businesses

How the Calculator Works

No black box. Here's exactly how we calculate your paint estimate.

The Calculation

Step 1: Net Area = Wall + Ceiling - (Doors × 20) - (Windows × 17.5)

Step 2: Primer = (Net Area ÷ Primer Coverage Rate) × 1.10 waste

Step 3: Paint Coats = 2 (or 3 for color change)

Step 4: Paint = (Net Area ÷ Paint Coverage Rate) × Coats × 1.10 waste

Why 20 sq ft per door? Standard interior door is 6'8" × 2'8" (about 18 sq ft) plus the frame area you don't paint. Windows average 3×5 ft (15 sq ft) plus trim.

Key Assumptions

  • •10% waste factor: Accounts for roller absorption, brush waste, drips, and touch-ups
  • •Two coats standard: Industry best practice for proper coverage and durability
  • •Three coats for color change: Going dark to light requires extra coverage to block bleed-through
  • •Half-gallon rounding: Results round to nearest 0.5 gal; shopping list rounds up to whole gallons

What This Calculator Doesn't Include

  • • Paint for trim, doors, or cabinets (different calculation)
  • • Extremely porous surfaces (bare concrete, new stucco)
  • • Spray application (uses 20-30% more paint)
  • • Varying paint quality (premium paint covers better)
  • • Dramatic color changes (dark to white may need 4+ coats)

Tip: When in doubt, buy an extra gallon. Unopened paint can be returned, and having touch-up paint is always useful.

Last updated: January 2026

Coverage rates based on Sherwin-Williams, Behr, and Benjamin Moore specifications.

Built by: Blessed Arc Media

Web design for home service businesses.

How Do I Use This Calculator?

Access this tool instantly from your phone, or add it to your website to help your audience.

Save This Tool for Quick Access

Open this tool anytime, just like a calculator on your phone. No app to download.

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Copy the direct link

https://blessedarcmedia.com/t/paint-calculator
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Tap your home screen icon or bookmark. Works just like opening the calculator on your phone.

What Makes This Calculator Different

Most paint calculators assume 400 square feet per gallon on smooth walls. This one adjusts for textured surfaces like orange peel, knockdown, and stucco, adds 10% for waste, and gives you a ready-to-use shopping list.

What makes this different

Surface Texture Adjustment

Textured walls absorb more paint than smooth drywall. This calculator adjusts coverage rates based on your actual surface — from smooth walls to stucco and brick.

No surprise shortages

Built-In Waste Factor

Paint is lost to roller nap, brush absorption, drips, and touch-ups. We add 10% automatically so you don't run out mid-project and have to make another store run.

Ready for the store

Instant Shopping List

Get a ready-to-use shopping list rounded up to whole gallons. Copy it to your phone or download a PDF with all your project details and a coverage disclaimer.

How Much Paint for Common Rooms?

Quick estimates for typical rooms. Your results may vary based on texture, doors, windows, and paint quality.

Bedroom (12×12)~400 sq ft walls, 8' ceiling
2 gal paint
Living Room (16×20)~576 sq ft walls, 8' ceiling
3 gal paint
Bathroom (8×10)~288 sq ft walls, 8' ceiling
1-2 gal paint
Kitchen (12×16)~448 sq ft walls, minus cabinets
2 gal paint
Master Bedroom (14×16)~480 sq ft walls, 8' ceiling
2-3 gal paint
Hallway (4×20)~384 sq ft walls, 8' ceiling
2 gal paint

Note: These estimates assume smooth drywall, 2 coats, and include waste factor. Textured walls, color changes, or painting ceilings will increase quantities.

Common Questions About Paint Coverage

Everything you need to know about calculating paint quantities.

Enter your wall and ceiling square footage, number of doors and windows, and select your surface texture. The calculator subtracts door and window areas (20 sq ft per door, 17.5 sq ft per window), applies coverage rates based on texture, adds 10% for waste, and rounds to the nearest half gallon. If you're doing a dark-to-light color change, it adds an extra coat.

On smooth drywall, one gallon covers about 350-400 square feet per coat. Textured surfaces absorb more paint — orange peel covers about 300-350 sq ft, knockdown 250-300 sq ft, popcorn/heavy texture 200-250 sq ft, and stucco/brick only 150-200 sq ft per gallon.

You need primer for new drywall, drywall repairs, bare wood, stained surfaces, or if you're making a dramatic color change. If you're painting over a similar color on previously painted, clean, non-glossy walls, you can often skip primer or use a paint-and-primer-in-one.

Two coats ensure even coverage, hide the old color completely, and provide better durability. The first coat soaks in more, while the second coat builds the protective film. Going from dark to light colors often requires three coats — this calculator accounts for that when you check the 'Color Change' option.

Most paint stores accept returns of unopened gallons within 30 days. Keep your receipt. Having a little extra is actually good — you can use it for touch-ups later, and paint colors can vary slightly between batches.

A typical 12×12 bedroom with 8-foot ceilings has about 400 square feet of wall space. After subtracting a door and two windows, you'll need roughly 2 gallons of paint for two coats on smooth walls. Textured walls need more — use this calculator for an exact estimate based on your surface type.

Measure the length of each wall and multiply by the ceiling height. For a 12×14 room with 8-foot ceilings: (12+14+12+14) × 8 = 416 sq ft of wall space. Don't worry about subtracting doors and windows manually — this calculator does that for you.

Textured surfaces have more surface area than smooth walls. A knockdown texture can have 30-40% more actual surface area than a flat wall, which means more paint is needed to cover it. Using smooth-wall coverage rates on textured walls will leave you short.

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