How to work out how much paint you need
Paint is sold by coverage, not by room size, so the trick is turning your room into square feet of wall. Here is the same math the calculator runs, using the values it opens with: a 14 x 10 room with 8 ft ceilings, one door, two windows, light texture and two coats.
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1
Find the perimeter
Add the length and width of the room and double it. (14 + 10) x 2 = 48 ft of wall all the way around.
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2
Multiply by the ceiling height
48 ft times an 8 ft ceiling gives 384 sq ft of wall. Measure the real height: many newer homes have 9 ft ceilings, which adds an eighth more wall.
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3
Subtract doors and windows
Take off about 21 sq ft per door and 15 sq ft per window. 384 − 21 − 30 leaves 333 sq ft to paint. Skip this step for small windows; the extra paint is cheap insurance.
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4
Multiply by coats, divide by coverage
333 sq ft x 2 coats = 666 sq ft. Divided by 350 sq ft per gallon, that is 1.9 gallons. Round up and buy 2 gallons.
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5
Price the job
2 gallons at $42 is $84. A roller kit, tray, brush, a roll of tape, a drop cloth and spackle add $56, for a total of $140 and about 5 hours of work.
Tick "Paint the ceiling" and the calculator adds the ceiling area (14 x 10 = 140 sq ft), two coats at 400 sq ft per gallon. That is 0.7 gallons, so one gallon of flat ceiling paint. Tick "Use primer" and it adds one coat over the walls and ceiling: 473 sq ft at 300 sq ft per gallon is 1.6 gallons, so 2 gallons. With both boxes on, the room comes to $243 and about 10 hours.
How far does a gallon go?
Coverage on the can assumes smooth, primed walls and a roller with the right nap. Rough or thirsty surfaces take more.
| Surface | Sq ft per gallon |
|---|---|
| Smooth, previously painted wall | 350–400 |
| Light texture (orange peel, knockdown) | 300–350 |
| New drywall without primer | 250–300 |
| Brick, stucco, heavy texture | 200–275 |
A 3/8 inch roller nap suits smooth walls. Light texture takes a 1/2 inch nap, and brick or stucco a 3/4 inch nap or more. A thicker nap holds more paint, which is part of why rough walls use more per square foot.
Paint needed for common room sizes
8 ft ceilings, one door, two windows, two coats, light texture. Tap a size to load it into the calculator.
| Room | Wall area | What to buy |
|---|---|---|
| 10 x 10 | 269 sq ft | 2 gallons |
| 10 x 12 | 301 sq ft | 2 gallons |
| 12 x 12 | 333 sq ft | 2 gallons |
| 12 x 14 | 365 sq ft | 2 gallons + 1 quart |
| 14 x 16 | 429 sq ft | 2 gallons + 2 quarts |
| 16 x 20 | 525 sq ft | 3 gallons |
| 20 x 20 | 589 sq ft | 3 gallons + 2 quarts |
Two quarts cost more than half a gallon, but they spare you a can that sits in the garage for ten years. If you expect touch-ups, round up to the next full gallon instead.
Which sheen goes where
Sheen changes how a wall looks and how well it stands up to scrubbing. Glossier paint wipes clean more easily but shows every dent and patch.
| Sheen | Best for |
|---|---|
| Flat or matte | Ceilings, adult bedrooms, walls with flaws to hide |
| Eggshell | Living rooms, dining rooms, most bedrooms |
| Satin | Hallways, kids' rooms, kitchens, laundry rooms |
| Semi-gloss | Trim, doors, cabinets, bathrooms |
The calculator covers walls and, if you tick it, the ceiling. Trim is separate: a quart of semi-gloss usually covers the baseboards, door casing and window trim of a bedroom.
What it costs: DIY vs. hiring a painter
Labor is most of a painter's price, usually 70% to 85% of the bill. Painters charge about $1 to $3 per square foot of wall, or $20 to $50 an hour, and many set a minimum of $250 to $500 per job. Ceilings add about $1 to $2 per square foot and trim about $1 to $4 per linear foot. The DIY column is this calculator's total for walls only, with the default $42 paint and new tools.
| Room | DIY, walls | Pro, walls | Pro, walls, ceiling, trim |
|---|---|---|---|
| 10 x 10 | $140 | $320–$1,200 | $640–$2,400 |
| 12 x 12 | $140 | $380–$1,400 | $770–$2,900 |
| 14 x 14 | $181 | $450–$1,700 | $900–$3,400 |
| 20 x 20 | $239 | $640–$2,400 | $1,300–$4,800 |
A single bedroom is a good DIY job: one weekend, few tools, and the savings are several hundred dollars. Hiring out makes more sense for stairwells and ceilings over 10 ft, rooms that need real drywall repair, and whole-house jobs where a crew finishes in days what takes you weeks. Ask for quotes that spell out coats, prep, primer and who buys the paint.
Tips from the trade
- Prep is half the job. Wash greasy kitchen and bathroom walls, fill nail holes, sand the patches smooth and wipe off the dust. Paint does not hide bumps; it highlights them.
- Spot-prime patches. Spackle soaks up paint differently from the wall around it and shows as a dull spot, called flashing. A dab of primer on each patch prevents it.
- Mix your cans together. Even tinted at the same store, two gallons can differ a little. Pour them into one bucket and stir, a step painters call boxing.
- Cut in, then roll, one wall at a time. Brush the corners and edges, then roll that wall while the brushed paint is still wet. Rolling over a dry cut line leaves a visible frame.
- Wait the full recoat time. The label gives it, often a few hours for latex. Cool or humid rooms take longer, and a second coat over soft paint can peel up.
- Pull the tape at an angle once the last coat is dry to the touch. If paint bridges the tape and the wall, score the edge with a utility knife first.
- Keep a little paint for touch-ups. Write the room, color and date on the lid, and store it where it won't freeze.
If your home was built before 1978, assume the old paint may contain lead until a test says otherwise. Washing and painting over sound paint is fine. Sanding, scraping or heat-stripping it is where the risk starts, and the EPA's lead-safe practices apply.
Common questions
How much paint do I need for a 12x12 room?
A 12x12 room with 8-foot ceilings, one door and two windows has about 333 square feet of wall. Two coats at 350 square feet per gallon need about 1.9 gallons, so buy 2 gallons. Add about 1 gallon of flat paint if you also paint the ceiling.
How many square feet does a gallon of paint cover?
One gallon covers about 350 to 400 square feet on smooth, primed walls. Textured walls, brick and fresh drywall soak up more paint, dropping coverage to around 200 to 300 square feet.
Do I need two coats of paint?
Plan on two coats when changing color, covering a dark shade or painting new drywall. One coat can be enough when refreshing the same color with a quality paint.
When should I use primer?
Use primer on new drywall, patched spots, glossy surfaces, stains and when going from dark to light colors. Paint-and-primer products help but do not replace primer on bare drywall.
Is it cheaper to buy a 5-gallon bucket of paint?
Usually yes once you need more than about 4 gallons of one color. A 5-gallon bucket typically costs about the same as four and a half single gallons, and the calculator switches to buckets when that saves money.
How much does it cost to paint a room?
Doing it yourself costs about $140 to $300 for paint and supplies for a typical bedroom. A painter charges about $300 to $1,000 for the walls of one room, or more with the ceiling and trim, because labor is 70% to 85% of the price.
Sources and assumptions
The calculator uses the same rules of thumb painters and paint makers publish. Prices are typical US prices checked in October 2026 and change by region, store and season. Every paint price can be edited.
- Coverage per gallon (about 350 to 400 sq ft on smooth walls, less on texture) follows the coverage listed on major brands' product data sheets and their own estimators, such as the Sherwin-Williams paint calculator and the Benjamin Moore paint calculator.
- Painter prices (room costs by size, $1 to $3 per sq ft of labor, $20 to $50 an hour, minimum job fees, ceiling and trim add-ons, and $15 to $50 per gallon for paint) come from HomeGuide, cost to paint a room (February 2026), which compiles quotes homeowners received.
- Openings: a standard interior door is counted as 21 sq ft (3 x 7 ft) and a window as 15 sq ft.
- Ceiling and primer: ceiling paint at 400 sq ft per gallon for two coats; primer as one coat at 300 sq ft per gallon. Default prices: $42 per gallon of wall paint, $32 for flat ceiling paint, $28 for primer, and a 5-gallon bucket at the price of 4.4 gallons.
- Labor time: about 150 sq ft per hour per coat for a DIY painter, plus an hour for setup and cleanup.
- Can sizes: the shopping list buys the cheapest mix of 5-gallon buckets, gallons and quarts that covers the job, so you are never told to buy 1.9 gallons.
- Older homes: if your home was built before 1978, sanding or scraping old paint can release lead dust. Read the EPA's lead-safe renovation guidance first.