When you start a painting project, one of the first challenges is figuring out how much paint you really need. Buy too little, and you’ll find yourself halfway through the job rushing back to the store. Buy too much, and you’ll waste money and space storing leftover cans.
The simplest solution? Use a paint calculator. Our free Paint Logs Wall Paint Calculator helps you estimate paint needs based on your wall dimensions, doors, windows, ceiling, and the number of coats.
How Much Paint Do I Need?
Why You Need a Paint Calculator
Whether you’re painting a bedroom, kitchen, bathroom, or the entire exterior of your house, guessing your paint needs often leads to frustration. A paint calculator interior or paint calculator exterior saves you from miscalculations.
Major brands like the Sherwin Williams paint calculator, Dulux paint calculator, Benjamin Moore paint calculator, Behr paint calculator, Boysen paint calculator, Asian Paints paint calculator, and Bunnings paint calculator all use the same principle:
- Measure your walls
- Subtract windows and doors
- Choose the number of coats
- Factor in ceilings if needed
The Paint Logs wall paint calculator works similarly
, but is simplified, free, and available online.
How to Calculate Paint Coverage (Step by Step)
1. Measure Your Walls
- Take the width and height of each wall.
- Multiply width × height = wall area.
- Do this for every wall.
This is the core of a paint calculator square feet or paint calculator m² approach.
2. Add Ceilings if Needed
- A ceiling paint calculator uses room width × length.
- Most ceilings need at least one coat, sometimes two.
3. Subtract Cutouts
- Subtract 20 square feet for each door and 15 square feet for each window.
- Some calculators, like the Home Depot paint calculator or Bunnings paint calculator, skip cutouts and simply add extra wastage.
4. Add Wastage
- Always add 10–15% to cover spills, touch-ups, and absorption.
- This is sometimes built into tools like the Sherwin Williams paint calculator.
5. Choose the Number of Coats
- Most interior projects need 2 coats.
- For darker colors or textured walls, 3–4 coats may be necessary.
Quick Estimates: How Much Paint for Each Room
If you don’t want to measure every wall, you can use quick averages. These are paraphrased estimates based on standard room sizes and coverage (1 gallon = ~350 sq ft):
Bathrooms
| Room | Floor Size | Wall Space | Paint Needed |
|---|---|---|---|
| Powder Room | 20 sq ft | ~120 sq ft | 1 gallon |
| Small Bathroom | 40 sq ft | ~110 sq ft | 1 gallon |
| Medium Bathroom | 120 sq ft | ~250 sq ft | 2 gallons |
| Large Bathroom | 160 sq ft | ~320 sq ft | 2 gallons |
Tip: Bathrooms often have less wall space due to fixtures, so a paint calculator interior may show lower totals.
Kitchens
| Room | Floor Size | Wall Space | Paint Needed |
|---|---|---|---|
| Small Kitchen | 100 sq ft | ~240 sq ft | 2 gallons |
| Medium Kitchen | 200 sq ft | ~380 sq ft | 2 gallons |
| Large Kitchen | 300 sq ft | ~515 sq ft | 3 gallons |
Note: Kitchens usually need more durable finishes like eggshell or semi-gloss.
Bedrooms
| Room | Floor Size | Wall Space | Paint Needed |
|---|---|---|---|
| Small Bedroom | 150 sq ft | ~345 sq ft | 2 gallons |
| Medium Bedroom | 200 sq ft | ~405 sq ft | 3 gallons |
| Large Bedroom/Suite | 300 sq ft | ~565 sq ft | 4 gallons |
Bedrooms typically have the largest wall surface to cover, so a wall paint calculator is especially useful here.
Interior vs Exterior Paint Calculations
Interior Paint Calculator
- Designed for smooth, even walls.
- Works in square feet or square meters.
- Perfect for living rooms, bedrooms, kitchens, and bathrooms.
Exterior Paint Calculator
- Exterior surfaces (siding, stucco, brick) require more paint because of rough textures.
- One gallon may only cover 250–300 sq ft outdoors.
- Many brands (Dulux, Jotun, Behr) provide specific exterior paint calculators.
If you’re outside the U.S., you may also see tools labeled paint calculator UK, paint calculator Australia, or paint calculator Bunnings that measure in square meters.
Paint Coverage by Brand
Every paint brand provides its own calculator, but the math remains the same. Here’s how the big names describe their tools:
- Sherwin Williams Paint Calculator → interior & exterior estimates with wastage factored in.
- Behr Paint Calculator → includes ceiling paint estimates.
- Benjamin Moore Paint Calculator → great for room-by-room planning.
- Dulux Paint Calculator → popular in the UK and Australia.
- Boysen Paint Calculator → widely used in Asia.
- Jotun Paint Calculator → focused on exterior and industrial surfaces.
- Asian Paints Calculator → often linked with design tools for interior décor.
The Paint Logs Paint Calculator gives you the same accurate results without brand bias.
Cost Estimation and Painting Budgets
A paint coverage calculator tells you the amount of paint. But if you’re budgeting, you’ll also want a painting cost calculator.
Interior Paint Cost Calculator
- Average: $2–$6 per sq ft including labor.
- Use an interior painting cost calculator to get closer estimates.
- Regional tools include:
- Painting cost calculator Australia
- Painting cost calculator UK
- Interior painting cost calculator Canada
Exterior Paint Cost Calculator
- Average: $1.50–$4 per sq ft (labor costs can double).
- A painting estimate calculator helps you prepare for seasonal jobs.
Specialty Calculators
- Interior paint quote calculator
- Interior paint bid calculator
- Commercial interior painting cost per square foot calculator
These help contractors and homeowners alike plan accurately.
Paint Calculation Formula
If you’d rather do the math yourself, here’s the paint calculation formula most tools use:
Total Paint Needed = (Wall Area + Ceiling Area – Cutouts + Wastage) × Number of Coats ÷ Coverage Rate
Where:
- Coverage Rate = 350 sq ft per gallon (32 m² per 4 liters) on smooth walls.
This formula is the foundation of every paint calculator square footage calculator, whether from Home Depot, Dulux, Sherwin Williams, or Bunnings.
Conclusion
A good paint calculator removes guesswork and ensures your project runs smoothly. Instead of stressing over gallons and square footage, let the numbers guide you.
The Paint Logs Paint Calculator is a free, easy-to-use tool that works for:
- Square feet and square meters
- Interior and exterior projects
- Walls and ceilings
Whether you’d normally use a Sherwin Williams paint calculator, a Dulux paint calculator, or a Behr paint calculator, the math is the same. Our tool gives you accurate results instantly.
FAQs
1. How does a paint calculator work?
It multiplies wall height × width, subtracts doors and windows, factors in coats, and gives you gallons or liters needed.
2. How much area does 1 gallon of paint cover?
About 350 sq ft indoors on smooth walls, and 250–300 sq ft outdoors on textured surfaces.
3. Should I subtract windows and doors?
Yes. Subtract 20 sq ft per door and 15 sq ft per window for accuracy.
4. How many coats of paint should I plan?
Most rooms need 2 coats. Dark colors or rough walls may need 3–4 coats.
5. Do I need a different calculator for exterior paint?
Yes. Exterior surfaces absorb more paint, so coverage rates are lower than indoors.
6. Can a paint calculator estimate costs too?
Some do. Multiply gallons needed × price per gallon, and add labor if hiring painters.
7. Should I round up or down when buying paint?
Always round up to have extra for touch-ups and avoid running out mid-project.