Interior Paint Calculator: How Much Paint Do I Need?

An interior paint calculator is crucial to planning your next painting project. Enter a few measurements, and our room painting calculator can tell you the paint needed for the room size and estimate how much paint is needed (gallons of paint coverage).

  • Accuracy: Estimating “eyeball” interior paint coverage might leave you with gallons of excess paint or a half-finished room. An interior paint calculator helps you measure exactly how much you need, down to the last drop.
  • Cost-Effective: Knowing the exact amount minimizes waste and ensures you only buy what is necessary, helping you stick to your budget.

Looking to hire a professional? Check out our House Painting Cost Estimator.

Interior Painting Calculator - Square Feet

Interior Painting Calculator - Square Feet

How much paint will you need?


You will need approximately gallons of primer paint and gallons of finish wall paint per coat.


You will need approximately gallons of ceiling paint per coat.


You will need approximately gallons of trim paint per coat.

Doors and Windows

You will need approximately gallons of the door and window paint per coat.

* Disclaimer: The coverage and cost calculations are estimates only and do not consider all possible factors. Home Inspection Insider provides this paint estimate and cost calculator for informational purposes only. For best results, verify your measurements before you purchase paint. We recommend you obtain cost estimates and verify credentials from three qualified contractors before making a hiring decision.  

interior paint calculator: how much paint do you need

Understanding Square Footage in Paint Calculations

Interior wall paint coverage doesn’t vary much between brands. However, it can vary based on the paint finish. The estimated interior paint coverage per gallon is 350 to 400 square feet (one coat) or 175 to 200 square feet for two coats.

You stand in your room, tape measure in hand, ready to conquer the task ahead. Understanding square footage is the cornerstone of your painting project. It’s the difference between a professional finish and a patchy outcome. Here’s how you make sense of it all:

  • Height x Width: Grab your tape measure and note the height and width of each wall. Multiply these figures to get the area in square feet. It’s your canvas, your domain.
  • Account for the Unusual: Got a fireplace? Built-in shelves? These subtract from your total square footage. You’re a detail-oriented planner, after all.

Each measurement, each calculation, brings you closer to that perfect finish. You’re considering gallons of paint per square foot, pondering paint quality and coverage. As you juggle these details, remember: the precision you apply here reflects the quality you’ll see on your walls.

Using an Interior Paint Calculator

You’re now at the heart of your project, poised to use the interior paint calculator for square feet. This wall paint estimator isn’t just about punching numbers; it’s about envisioning the end result and meticulously mapping your path there. Follow these steps, and you’ll navigate this crucial phase with confidence and precision.

Enter Your Room Dimensions:

  • Length, Width, and Height: Input these into the calculator. This isn’t just data entry; it’s the first brushstroke on your canvas.
  • Acknowledge Every Corner: No worries if your room isn’t a perfect rectangle. Adjust for alcoves and recesses. You’re a detailed painter, not a corner cutter.

Account for Doors and Windows:

  • Subtract the Space: Doors and windows don’t need paint, so deduct their area from the total. It’s about being resourceful and accurate.
  • Detail Matters: Measure each window and door precisely. Even the smallest detail can impact your paint needs.

Choose Your Paint Quality:

  • Options Galore: Basic, standard, or premium? Your choice affects coverage and longevity. You’re not just choosing paint; you’re choosing the ambiance and mood for your room.
  • Consider the Finish: Glossy, matte or satin? Each has its charm and function. You’re setting the stage for the room’s future character.

Determine the Number of Coats:

  • Single or Multiple: One coat might suffice, but two ensure depth and evenness. You’re building layers, not just covering walls.
  • Think Long-Term: More coats mean more durability. You’re investing in your home’s future beauty.

Calculate Prep Work:

  • Smooth and Ready: Will you clean, sand, or prime? Each step ensures your paint adheres better and lasts longer. You’re not just painting; you’re preparing a masterpiece.
  • Time and Effort: Good prep might take time, but it elevates the end result. You’re a craftsman, ensuring every detail is perfect.

Paint Coverage Essentials

Understanding paint coverage is crucial as you stand before the potential of bare walls. This isn’t merely about aesthetics; it’s about efficiency and effectiveness. With a keen eye on the details, you’ll ensure every square foot of your space is perfectly covered.

Grasping Coverage Rates:

  • Gallons Per Square Foot: A gallon typically covers 350 to 400 square feet. You’re not just buying paint; you’re investing in coverage.
  • Quality Counts: Higher-quality paint often means better coverage and durability. You’re choosing resilience and richness with every selection.

Factors Affecting Coverage:

  • Surface Texture: Rough surfaces drink more paint. You’re not just coating a wall but navigating its unique landscape.
  • Color Depth: Darker shades might require more coats. You’re not just changing colors; you’re crafting depth and mood.
interior painting wall

Estimating Paint Quantities for Different Room Sizes

Your project is unique, and so is every room you’re transforming. Whether it’s a compact bathroom or a sprawling living area, your approach adjusts to fit the space. You’re not just a painter but a planner, tailoring a strategy for each area.

Case Studies for Common Room Sizes:

  • Small Spaces: They might need less paint, but precision is key. You’re maximizing impact in minimal areas.
  • Large Areas: Bigger rooms require more paint and more patience. You’re not just covering more ground but creating a larger canvas.

Multiple Coats and Primer Needs:

  • Should You Use a Primer: Primer ensures your paint adheres well and shines true. You can skip primer if the paint color is similar or going darker, but you should use a primer first if you’re painting over a dark color.
  • Deciding on Coats: Professional painters recommend two coats for more color vibrancy and protection. You should apply a primer and two coats of high-quality paint when painting over darker colors.

Common Mistakes to Avoid

As you approach the final stages of your painting project, being aware of common pitfalls can make the difference between a satisfactory outcome and a spectacular one. You’re not just finishing a task; you’re perfecting an art. Here’s how to sidestep potential issues and ensure a smooth, stunning finish:

Overlooking Prep Areas:

  • Skipping the Primer: Neglecting this crucial layer can lead to uneven color and poor adhesion. You’re not just priming a wall; you’re preparing a canvas.
  • Ignoring Surface Irregularities: Failing to patch and sand means your paint won’t look its best. You’re striving for perfection, not just coverage.

Misjudging Color and Texture:

  • Underestimating Color Impact: A shade might look different on a swatch than on a wall. Test your colors in the intended space to avoid surprises. You’re not just choosing a color; you’re setting a mood.
  • Forgetting About Finish: The glossiness of your paint can affect its appearance and durability. Consider your room’s use and lighting when choosing a finish. You’re not just selecting a sheen; you’re crafting an atmosphere.


How do you calculate square footage for interior painting?

To calculate square footage for interior painting, measure the length and width of each wall in feet. Multiply the length by the width for each wall, then sum up all the measurements. This will give you the total square footage for interior painting.

How much paint do I need for a 2000 square foot house interior?

You will need approximately 10 to 12 gallons of paint for two coat coverage of a 2000 square foot house interior.

How many square feet does 1 gallon of paint cover?

A gallon of paint coverage equals 350 to 400 square feet for one coat. For two-coat coverage, a gallon of paint coverage is about 175 to 200 square feet.

How many square feet will a 5 gallon bucket of paint cover?

A 5-gallon paint bucket typically covers around 1,500 square feet for one coat of surface coverage.

Can I use an interior paint calculator for textured walls?

Yes, but add 10-20% more paint to your estimate to account for the extra surface area the texture creates.

Does the type of paint (oil or latex) affect the coverage?

Yes, oil-based paints generally cover more area but require more prep and drying time than latex-based paints.

How should I adjust calculations for a room with vaulted ceilings?

Adjust the calculations for a room with vaulted ceilings by factoring in the additional volume of the higher ceiling. The formula for calculating the volume of a room is length × width × height. Include the height of the vaulted ceiling when determining the room’s height for accurate calculations.

What if I’m changing from a dark to a light color?

Plan for an additional coat or use a primer to cover dark shades to ensure proper coverage and color accuracy.

How does the sheen of the paint affect the amount I need?

Higher-sheen paints often cover better and may require slightly less product, but the difference is typically minimal. Higher sheen paints show more imperfections, making prep work critical.

Do I need to adjust the amount of paint for a primer if I’m using a paint and primer in one?

No, you do not need to adjust the amount of paint for a primer if you’re using a paint and primer in one. You may need three coats of paint to prevent peeking when covering darker colors.


Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.