Paint Calculator

Why a Paint Calculator Saves You Money

A single gallon of premium interior paint runs $40 to $70, so guessing wrong gets expensive fast. Over-buy by two gallons and you've thrown away $80 to $140 on cans that dry out in the garage. Under-buy and you face a second trip to the store — plus the risk of a slightly mismatched batch that shows up as a faint stripe on a sunny wall. This free paint calculator removes the guesswork: enter your room and it tells you exactly how many gallons to buy before you ever pick up a brush.

The savings go beyond paint itself. Knowing your real square footage up front means you buy the right number of roller covers, the right amount of tape, and one primer purchase instead of two. For a whole-house repaint, accurate estimating across every room easily saves $100 or more — money far better spent on better paint that covers in two coats instead of three.

How to Use This Calculator

Three quick steps turn your tape-measure numbers into a shopping list:

1. Enter your room dimensions. Type in the room's length, width, and wall height in feet. Most homes have 8 ft ceilings; older homes and newer builds sometimes have 9 or 10 ft walls, which adds meaningful area.
2. Set doors, windows, and coats. Each door subtracts about 21 sq ft and each window about 15 sq ft. Pick your number of coats — two is standard — choose a finish, and toggle the ceiling on if you're painting it.
3. Review the gallon count and materials checklist. The calculator shows gallons needed, paintable area, and an estimated cost. The materials checklist below it rounds out your cart with rollers, brushes, tape, and primer.

Finishing fresh walls first? Size the board and mud with our drywall calculator. Papering an accent wall instead of painting it? Switch over to the wallpaper calculator, which uses the same room inputs to count rolls. Tiling a backsplash or tub surround instead? The tile calculator sizes tile, grout, and thinset for that surface.

How to Calculate Paint for a Room Manually

Want to check the math by hand? Follow these steps:

1. Measure the room perimeter: add the length and width, then double it — 2 × (length + width). A 12 × 12 room is 2 × (12 + 12) = 48 linear feet.
2. Multiply perimeter × wall height to get gross wall area. At 8 ft ceilings, 48 × 8 = 384 sq ft.
3. Subtract the openings: take off 21 sq ft for each door and 15 sq ft for each window. One door and two windows is 21 + 30 = 51 sq ft, leaving 333 sq ft.
4. If you're painting the ceiling, add length × width. A 12 × 12 ceiling adds 144 sq ft to the paintable total.
5. Multiply paintable area by your number of coats. Two coats on 333 sq ft is 666 sq ft of coverage to buy.
6. Divide by coverage — 350 to 400 sq ft per gallon for most latex paint. 666 ÷ 350 ≈ 1.9 gallons.
7. Round up to the nearest whole gallon. You can't buy a partial gallon, so call it 2 gallons and keep the leftover for touch-ups.

Paint Coverage by Finish Type

Sheen changes how far a gallon stretches. Use this table to match finish to room and adjust your estimate:

Common Paint Estimating Mistakes

Forgetting to deduct doors and windows. Skip the openings and you overestimate paintable area by 10 to 15% in a typical room — that's the difference between buying two gallons and needlessly buying three. The calculator subtracts them automatically, but if you measure by hand, don't forget this step.

Not accounting for extra coats on dark-to-light changes. Covering a deep navy or red with a pale color often takes three coats, not two — sometimes with a tinted primer underneath. Plan the coats honestly up front instead of running short with the wall half-finished.

Buying ceiling paint at wall coverage rates. Ceiling paint is thicker and formulated to resist drips and spatter, so a gallon covers closer to 300 sq ft, not 350 to 400. If you assume wall coverage, you'll come up short on the ceiling.

Ignoring primer on new drywall. Bare drywall and fresh joint compound soak up paint unevenly, dropping coverage by about 30% and leaving visible seams. A coat of PVA primer first seals the surface, evens out absorption, and actually saves a gallon of your finish color. Our drywall calculator helps you size that primer order alongside the board and mud.

Frequently Asked Questions

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

A 12×12 room with 8 ft ceilings has about 384 sq ft of wall area. After deducting one door (21 sq ft) and two windows (30 sq ft), you have 333 sq ft of paintable wall. Two coats at 350 sq ft per gallon works out to about 2 gallons.

How many coats of paint do I need?

Two coats is the standard for most repaints and gives the best color depth and durability. Use three coats when going from a dark color to a light one or covering stains. A single coat only works with paint-and-primer products over a very similar color.

Does paint finish affect how much I need?

Yes, slightly. Flat paint spreads farthest at about 400 sq ft per gallon, while semi-gloss and high-gloss cover less — 300 to 350 sq ft — because they are thinner and need an even film. Choosing a higher sheen can nudge your gallon count up on a large room.

Do I need primer before painting?

Prime any bare drywall, patched areas, or major color changes. Raw drywall drinks up paint and needs a dedicated PVA primer first, or your coverage drops by about 30%. For repaints in a similar color, a modern paint-and-primer product usually skips the separate step.

How much does it cost to paint a room yourself?

A typical 12×12 room costs roughly $80 to $200 in materials: about 2 gallons of paint ($80–$140) plus rollers, brushes, tape, and drop cloths ($40–$60). Hiring a pro for the same room usually runs $300 to $800 depending on prep and local labor rates.