Paint Quantity Calculator

How to Use the Paint Quantity Calculator

Wondering how much paint you need for a bedroom, living room, or another interior space? Our free Paint Quantity Calculator helps you estimate the amount of paint required based on your room dimensions, wall openings, number of coats, and paint coverage.

Simply enter your measurements above to calculate the paintable surface area, total coverage needed, estimated paint volume, and suggested purchase quantity.

What Measurements Do You Need?

The calculator supports feet/inches and metric measurements.

Important: This tool is designed for rectangular rooms with equally sized door openings and equally sized window openings. For irregular rooms, measure separate sections and calculate them individually.

If you’re unsure about typical bedroom dimensions, see our Standard Bedroom Size Guide.

How Much Area Does One Gallon of Paint Cover?

One gallon of interior wall paint commonly covers approximately 350–400 square feet with one coat, depending on the product and surface.

According to Sherwin-Williams’ paint calculator guidance, actual coverage can vary with surface texture, application method, and paint formulation.

These are general estimates for wall paint, not guaranteed coverage rates.

The calculator starts with a default coverage of 350 square feet per gallon. For a more accurate estimate, replace that value with the coverage listed on your chosen paint product.

Understanding Your Paint Calculator Results

The calculator provides four results to help you plan your purchase.

1. Paintable Area per Coat

This is the surface area that will receive paint after subtracting the entered door and window openings.

For a rectangular room:

Gross wall area = 2 × (Room length + Room width) × Wall height

The calculator subtracts the total area of door and window openings.

If you select Include ceiling, it also adds the ceiling’s surface area.

2. Total Coverage Needed

The calculator multiplies the paintable area by your selected number of coats.

For example, if your room has 300 square feet of paintable wall area:

• One coat requires 300 square feet of coverage.
• Two coats require 600 square feet of coverage.
• Three coats require 900 square feet of coverage.

The number of coats depends on the previous paint color, surface condition, selected product, and desired finish.

3. Estimated Paint Volume

The calculator divides the total coverage required by your paint’s specified coverage rate, then applies your selected extra allowance.

Formula:

Estimated gallons = (Total coverage area ÷ Coverage per gallon) × (1 + Extra allowance ÷ 100)

For example, a project requiring 700 square feet of coverage with paint rated at 350 square feet per gallon and 10% extra allowance needs approximately 2.2 gallons.

This allowance helps account for ordinary application losses and touch-ups, but heavily textured or porous surfaces may require more.

4. Suggested Purchase Volume

The tool rounds the estimated paint requirement upward to a planning quantity.

This helps you avoid purchasing less paint than the estimate requires.

However, the displayed quantity may not match available retail container sizes. Check whether your preferred paint is sold in quarts, gallons, or larger containers before purchasing.

Example: How Much Paint for a 12 × 10-Foot Room?

Consider a bedroom with the following measurements:

Estimated results:

• Gross wall area: 352 sq. ft.
• Paintable wall area after openings: approximately 322.2 sq. ft.
• Total coverage for two coats: approximately 644.4 sq. ft.
• Estimated paint requirement, including 10% extra: approximately 2.03 gallons.
• Rounded suggested purchase volume: 2.25 gallons.

This example uses the calculator’s default assumptions.

Actual consumption may differ based on wall texture, paint quality, roller type, and surface preparation.

If you’re planning the project yourself, our How Long Does It Take to Paint a Room? guide explains preparation time, coat application, drying intervals, and realistic project timelines.

Should You Include the Ceiling and Primer?

Ceiling Paint

Select Include ceiling when you want to estimate walls and ceiling together.

The calculator uses the same number of coats and paint coverage rate for both surfaces.

If you plan to use a separate ceiling paint with a different coverage rate, calculate that material separately for a more accurate shopping estimate.

Primer

Primer is not included as a separate material in this calculator.

Previously unpainted drywall, repaired surfaces, stains, and major color changes may require primer or additional preparation.

Primer coverage can differ from wall-paint coverage. Check the product specifications before buying.

Tips Before Buying Paint

A few checks can help prevent wasted paint or unexpected trips to the store.

• Confirm the coverage rate: Use the value printed on your selected paint product.
• Check the wall condition: Rough, porous, or heavily textured walls may absorb more paint.
• Plan the number of coats: Major color changes may require additional coats or an appropriate primer.
• Calculate different colors separately: Each color should have its own quantity estimate.
• Allow for touch-ups: Retaining some leftover paint can help with future repairs.
• Check caulk and repairs: Complete suitable surface preparation before painting.

If you’re sealing small gaps around trim or windows, our How Long Does Caulk Take to Dry? guide explains when different sealants may be ready for painting.

Safety note: Homes built before 1978 may contain lead-based paint. Sanding or disturbing older painted surfaces can create hazardous dust. Review the EPA’s lead-safe renovation guidance before undertaking preparation work on potentially lead-painted surfaces.

Frequently Asked Questions

How much paint do I need for a 12 × 12 room?

A 12 × 12-foot room with 8-foot walls has approximately 384 square feet of gross wall area. After subtracting door and window openings, two coats often require around 2 gallons or more, depending on coverage and extra allowance. Use the calculator for your actual dimensions.

How many square feet does one gallon of paint cover?

Many interior wall paints cover approximately 350–400 square feet per gallon with one coat. The actual coverage depends on the product, surface condition, and application method.

Do I need two coats of paint?

Two coats are a common starting point for interior repainting, but the requirement varies. Some projects need primer or additional coats, especially when covering a darker color or painting a porous surface.

Does this calculator include windows and doors?

Yes. You can enter the number and dimensions of your door and window openings. Their calculated areas are deducted from the gross wall area. The tool assumes openings of each type have equal dimensions.

Does the calculator include primer and ceiling paint?

It can include ceiling area when selected, using the same coverage rate and number of coats as the walls. Primer is not estimated separately, so calculate primer requirements using its own coverage specifications.

More Home Improvement Resources

Planning your paint quantity is just one step in preparing a room for a fresh look. Explore these related House Made Clear guides:

• Affordable Ways to Update a Living Room — Learn how wall paint, lighting, and furniture arrangement can refresh a room without a full renovation.
• How to Make a Dark Room Brighter Without Adding Windows — Explore paint colors, lighting, and interior adjustments that can make a room feel brighter.
• Free Home Planning Tools & Calculators — Explore more practical tools for room planning, furniture measurements, and home improvement.

Measure before you buy. Use the Paint Quantity Calculator above to estimate your paint requirements and plan your next painting project with greater confidence.

House Made Clear — Better Homes, Explained Clearly.