Paint Coverage Calculator — How Much Paint Do I Need?

Calculate Paint Needed

Enter your room or wall dimensions to find out exactly how much paint to buy. The calculator accounts for doors, windows, number of coats, and paint coverage rate.

Paint Coverage Rates by Type

Coverage varies significantly by paint type, finish, and surface texture. Use this table as a guide when choosing a coverage rate.

These are approximate ranges for smooth, primed surfaces. Porous, rough, or unpainted surfaces will reduce coverage by 15-30%. Always check the paint can label for manufacturer-specific coverage rates.

Standard Opening Sizes

Use these common sizes when subtracting doors and windows from your wall area.

How to Use This Calculator

1. Choose your mode: Use "Whole Room" to calculate all four walls at once from length, width, and height. Use "Individual Walls" if your walls vary in size or if you are only painting some walls.
2. Enter dimensions: Type your room or wall measurements. The default unit is feet; switch to meters if preferred.
3. Add openings: Add doors and windows to subtract from the total. Select a preset size or enter custom dimensions.
4. Set paint options: Choose the number of coats (two is standard) and a coverage rate. The default of 350 sq ft per gallon works for most interior latex paints.
5. Read results: The calculator shows total paint needed, number of cans to buy (rounded up), and a full area breakdown.

How It Works

The formula behind this calculator is straightforward:

Paint Needed = (Paintable Area x Number of Coats) / Coverage Rate

Where:

• Paintable Area = Total wall area (and ceiling if selected) minus the area of all doors and windows
• Number of Coats = How many layers of paint you will apply (typically 2)
• Coverage Rate = How many square feet one gallon of paint covers on a smooth surface (typically 350 sq ft)

For a room in "Whole Room" mode, total wall area is calculated as: 2 x (Length + Width) x Height. If you include the ceiling, the calculator adds Length x Width to the total. In "Individual Walls" mode, each wall is simply Width x Height.

Tips for Accurate Paint Estimation

When to add extra paint

• Textured walls: Stucco, knockdown, or orange-peel textures absorb more paint. Reduce your expected coverage by 15-30%.
• Dark-to-light color change: Going from dark to light? Plan on a coat of primer plus 2-3 topcoats.
• New drywall: Unpainted drywall is porous and soaks up more paint. Always prime first.
• Spray painting: Overspray waste can increase paint usage by 20-30% compared to roller application.

When you might need less paint

• Same color refresh: A single coat may suffice when painting over a similar color in good condition.
• High-quality paint: Premium paints with higher pigment density often cover in fewer coats.
• Smooth, primed surfaces: Already-painted smooth walls provide ideal coverage conditions.

Do I need primer?

Primer is essential in these situations:

• Painting over new, bare drywall or joint compound
• Covering dark colors with a lighter shade
• Painting over stains (water marks, smoke, or crayon)
• Switching between paint types (e.g., oil-based to latex)
• Painting bare wood, metal, or masonry

Paint-and-primer-in-one products are convenient for simple repaints but do not replace dedicated primer for challenging surfaces.

Frequently Asked Questions

How much paint do I need for a 12x12 room?

A 12x12 room with 8-foot ceilings has about 384 square feet of wall area. After subtracting a door (21 sq ft) and two windows (30 sq ft), you have roughly 333 square feet of paintable area. At 350 sq ft per gallon, you need about 1 gallon per coat, or 2 gallons for two coats.

How many square feet does a gallon of paint cover?

A gallon of standard interior latex paint covers approximately 350-400 square feet on smooth, primed surfaces. Coverage depends on paint quality, surface texture, color, and application method. Check the label on your specific paint for the manufacturer's estimate.

Do I need primer before painting?

Primer is recommended when painting over new drywall, dark colors, stains, or bare wood. If you are repainting a wall with a similar color and the existing paint is in good condition, you can often skip primer. For dramatic color changes, tinted primer saves topcoat layers.

How many coats of paint do I need?

Most painting projects need two coats for uniform coverage and accurate color. One coat may work when repainting with a very similar shade. Drastic color changes (especially dark to light) may require three coats or a primer coat plus two topcoats.

Should I buy extra paint?

Yes. Buy 10-15% more paint than your calculated amount to account for roller waste, touch-ups, and uneven application. Always round up to the next full can. Keep leftover paint stored properly for future touch-ups -- even small nicks and scuffs are easier to fix if you have matching paint on hand.

What is the difference between flat, eggshell, satin, and semi-gloss paint?

These terms describe the sheen (reflectivity) of the dried paint. Flat has no shine and hides imperfections but is hard to clean. Eggshell has a soft, low sheen suitable for living rooms and bedrooms. Satin is slightly shinier and more durable, good for hallways and kids' rooms. Semi-gloss is reflective and moisture-resistant, ideal for kitchens, bathrooms, and trim.

Does this calculator account for waste?

This calculator computes the theoretical paint needed and rounds up to full cans. It does not add a separate waste percentage. For best accuracy, buy one extra quart or consider the 10-15% buffer recommendation.

Does this calculator store my data?

No. All calculations run entirely in your browser. No data is sent to any server, and nothing is stored.

Related Tools

• Square Footage Calculator -- calculate area from room dimensions
• Deck Cost Calculator -- estimate materials for a deck project
• Gravel Calculator -- calculate gravel needed for landscaping
• Concrete Block Calculator -- estimate blocks for a wall
• Roof Pitch Calculator -- calculate roof angles and areas

Paint Coverage Calculator FAQ