Interior Paint Calculator

Calculate paint requirements for interior walls, ceilings, and trim. Accounts for doors, windows, and number of coats needed.

Interior Paint Calculator

Professional estimation based on industry standards

Room Measurements

Room 1

feet
feet
feet
Door 1
Window 1
Window 2

Paint Specifications

Wall Paint

💡 Standard Practice: New/unpainted surfaces get 1 coat primer + 2 coats paint. Previously painted surfaces typically need 2 coats of paint only.

Ceiling Paint

Calculation Standards:

  • • Industry coverage: 350-400 sq ft/gal (smooth surfaces)
  • • Primer coverage: 200-300 sq ft/gal
  • • Variable door/window sizes (10-40 sq ft)
  • • PCA & MPI professional standards
  • • Includes waste factors & adjustments

📚 Helpful Guides:

Frequently Asked Questions

How much paint does one gallon cover?

One gallon covers 350-400 square feet per coat on smooth drywall per PCA standards. Textured walls cover 300-350 square feet per gallon. Bare drywall or dramatic color changes require 250-300 square feet per gallon for first coat due to higher absorption.

How much does primer cover per gallon?

Primers universally cover less surface area than topcoats, standardizing at 200-300 square feet per gallon across all manufacturers. This reduced coverage ensures proper sealing and adhesion on bare or previously unpainted surfaces.

Should I deduct doors and windows from calculations?

Deduct openings larger than standard door size (20 square feet). Small windows (15 square feet) are often not deducted as they offset areas missed in corners and edges. For large window walls, deduct 50% of opening area as a practical compromise between accuracy and paint waste.

How many coats of interior paint do I need?

Most interior projects need 2 coats for uniform coverage and durability. Light colors over white primer may need 1-2 coats. Dark or bold colors require 2-3 coats. New drywall needs 1 coat primer plus 2 finish coats per manufacturer recommendations.

Industry Standards Referenced

Last verified: November 2025

PDCA - Painting & Decorating Contractors of America Standards(P1-P20 Standards)

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Industry standards for surface preparation, application methods, and quality benchmarks. Defines coverage rates, drying times, and coating specifications for professional painting.

Key Requirements:

  • •Surface prep: Walls must be clean, dry, and smooth before painting
  • •Primer required for: New drywall, repairs, dark-to-light color changes, stains
  • •Minimum 2 coats recommended for uniform coverage and durability
  • •24-hour drying time between coats at 70°F and 50% humidity
Applies to:All interior painting projects

Master Painters Institute (MPI) Standards(MPI Gloss Level Standards)

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Defines paint sheen levels and appropriate applications. Level 1 (Flat) to Level 7 (High Gloss). Higher gloss = more durable but shows imperfections more easily.

Key Requirements:

  • •Level 1-2 (Flat/Matte): Ceilings, low-traffic walls - 400 sq ft/gal
  • •Level 3-4 (Eggshell/Satin): Living areas, bedrooms - 375 sq ft/gal
  • •Level 5-6 (Semi-Gloss): Kitchens, bathrooms, trim - 350 sq ft/gal
  • •Level 7 (High-Gloss): Cabinets, doors, high-wear areas - 325 sq ft/gal
Applies to:Paint sheen selection and coverage estimation

ASTM D3276 - Guide for Painting Inspectors(ASTM D3276-15)

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Standard for paint inspection and quality control. Covers film thickness measurement, adhesion testing, and defect identification.

Key Requirements:

  • •Wet film thickness: 4-6 mils per coat typical
  • •Dry film thickness: 1.5-2 mils per coat minimum
  • •Coverage uniformity: Visual inspection for holidays (missed spots)
  • •Adhesion test: Cross-hatch or pull-off test for critical applications
Applies to:Quality control and professional inspection

Paint Quality Institute (PQI) Guidelines(Consumer Education Standards)

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Provides paint quality ratings and application best practices. Premium paints offer better coverage (fewer coats) and durability than economy paints.

Key Requirements:

  • •Premium paints: 350-400 sq ft/gal, better hide, one-coat coverage possible
  • •Mid-grade paints: 300-350 sq ft/gal, adequate hide, two coats standard
  • •Economy paints: 250-300 sq ft/gal, poor hide, may require 3+ coats
Applies to:Paint selection and coverage calculations

Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.

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Want to Learn More?

Paint & Decorating Retailers Association standards, 350-400 sq ft per gallon coverage rates, and primer requirements.

Read the Interior Paint Coverage Guide

How to Use This Calculator

  1. Enter room dimensions: Input length, width, and ceiling height.
  2. Subtract openings: Enter number of doors and windows.
  3. Select surfaces: Choose walls, ceiling, trim, or all.
  4. Review paint needed: See gallons per coat for each surface.

Interior Paint Coverage Standards

Standard coverage is 350-400 sq ft per gallon on smooth drywall. Textured surfaces reduce coverage to 250-300 sq ft/gal. Prime new drywall before painting.