How much paint do I need for a room?

Measure the wall perimeter, multiply by wall height for total area, subtract doors and windows, multiply by the number of coats, then divide by the paint coverage per gallon (check the label). For a typical 12 × 10 ft room with 8 ft ceilings and two coats, you need about 2 gallons.

How do I calculate wall area for paint?

Add the lengths of all walls to get the perimeter, then multiply by the wall height. For example, a 12 × 10 ft room has a perimeter of 44 ft, and with 8 ft ceilings that gives 352 sq ft of wall area.

How many coats of paint should I plan for?

Most projects need two coats for even coverage, especially when changing colors. If you are applying the same color over an existing coat in good condition, one coat may suffice.

Should I subtract doors and windows?

Yes. Subtract the approximate area of each door (about 21 sq ft) and window (about 15 sq ft) from the total wall area to avoid buying more paint than you need.

Does paint coverage vary by product?

Yes. Most paints cover 350–400 sq ft per gallon, but this varies by brand, finish, and surface type. Always check the manufacturer coverage on the paint can for the most accurate estimate.

Guide

How to Calculate How Much Paint You Need for a Room

Buying the right amount of paint saves money and avoids mid-project trips to the store. The calculation comes down to wall area, openings, and the number of coats you plan to apply. This guide walks through each step with a clear formula and a worked example.

Key Takeaways

Wall area is calculated as wall perimeter × wall height.
Subtract the area of doors and windows from the total wall area.
Check the paint can for its stated coverage per gallon — it varies by product.
Plan for two coats in most cases, especially when changing colors.
Use the NOVORY Paint Calculator for an instant estimate.

Calculate Paint

How to Calculate Paint Quantity

Paint estimation is an area calculation, not a volume calculation. You need the total wall surface area, minus the openings you will not paint, divided by the paint coverage per gallon.

1Measure the length of each wall and add them together to get the perimeter.
2Measure the wall height from floor to ceiling.
3Multiply perimeter × height to get total wall area in square feet.
4Subtract the area of doors (approx. 21 sq ft each) and windows (approx. 15 sq ft each).
5Check the paint label for coverage per gallon — typically 350–400 sq ft per gallon.
6Multiply the paintable area by the number of coats, then divide by coverage per gallon.

The Paint Calculation Formula

The core formula for wall area and paint quantity is:

Paint (gallons) = (Wall Area − Openings) × Coats ÷ Coverage per Gallon

Worked Example: 12 ft × 10 ft Room, 8 ft Ceilings

Let us calculate paint for a room that is 12 feet by 10 feet with 8-foot ceilings, one door, and two windows.

Step 1

Calculate the wall perimeter: 12 + 10 + 12 + 10 = 44 ft.

Step 2

Calculate wall area: 44 × 8 = 352 sq ft.

Step 3

Subtract openings: one door (≈ 21 sq ft) + two windows (≈ 30 sq ft) = 51 sq ft. Paintable area: 352 − 51 = 301 sq ft.

Step 4

Plan for two coats: 301 × 2 = 602 sq ft total coverage needed.

Step 5

Estimate gallons at 350 sq ft/gallon: 602 ÷ 350 ≈ 1.72 gallons. Round up to 2 gallons.

Common Mistakes

Not planning for a second coat — most projects, especially color changes, need at least two coats.
Using a single coverage number without checking the actual paint label — coverage varies by product and surface.
Forgetting to subtract doors and windows, which overstates the paintable area.
Ignoring the ceiling — if you are painting the ceiling, calculate it separately (Length × Width of the room).
Not accounting for textured walls, which absorb more paint than smooth walls.

Practical Tips

Always check the manufacturer coverage on the paint can — it is the most reliable number for that specific product.
Buy a little extra for touch-ups. A quart is usually enough for small corrections later.
Primer may be needed for drastic color changes or new drywall — factor it into your total.
If the room has a chair rail or wainscoting, calculate the upper and lower sections separately.
Use the NOVORY Paint Calculator to double-check your estimate and adjust for waste.