Paint: how much you need, inside and out
A gallon of wall paint covers roughly 350 square feet per coat on smooth, primed drywall, so paint is worked out from wall area, minus doors and windows, times the number of coats. A 12 x 12 ft room with 8 ft ceilings needs about 1.9 gallons for two coats on the walls, with one door and two windows taken off. Round up to whole gallons and keep what is left for touch-ups.
Here is everything we have on painting: calculators for rooms, whole-house exteriors, caulk and deck stain, the guides on coverage and sheen, and the mistakes that cost people a second trip to the store.
Gallons of paint by room size
Walls only, 8 ft ceilings, one door and two windows, at 350 square feet per gallon. Worked out by the paint calculator.
| Room (feet) | One coat (gallons) | Two coats (gallons) |
|---|---|---|
| 10 x 10 | 0.8 | 1.5 |
| 10 x 12 | 0.9 | 1.7 |
| 12 x 12 | 1.0 | 1.9 |
| 12 x 14 | 1.0 | 2.1 |
| 14 x 16 | 1.2 | 2.5 |
| 16 x 20 | 1.5 | 3.0 |
Interior walls and ceilings
Measure the room's length, width and ceiling height, count the doors and windows, and decide on coats. New drywall, a strong color change or a dark color over a light one usually needs a primer coat first, and the supplies calculator adds the primer, tape, rollers and caulk to the list.
Painting the outside of a house
Exterior paint is worked out from the wall area of the house, gables included, minus doors and windows. A one-story 40 x 30 ft house with 9 ft walls and two gables comes to 1,290 square feet and about 7.4 gallons for two coats. Rough siding drinks more paint than smooth, so lower the coverage figure for shingles or stucco.
Wallpaper instead of paint
Wallpaper is counted in rolls rather than gallons, and the pattern repeat decides the waste. The wallpaper calculator works from wall length and height, and the guide explains why you should buy every roll from one batch.
Decks and fences
Deck stain covers far less than wall paint, because bare wood soaks it up. The deck stain calculator includes railings and steps, and the coverage figure on the can is the one to use.
Every calculator for this topic
Guides
- Common Mistakes When Hanging Wallpaper (Rolls and Pattern Waste)Ordering too few rolls is the top wallpaper mistake. A room with 40 ft of wall, 8 ft high, needs 12 single rolls at 15% waste. See why pattern repeat matters.
- Common Mistakes When Painting a Room (and How Much to Buy)Buying paint for one coat, forgetting the ceiling or trusting the can label. A 12 × 12 ft room needs 1.9 gal for two coats on the walls, 2.7 with the ceiling.
- How Many Square Feet Does a Gallon of Paint Cover? ChartA gallon of paint covers about 350 square feet per coat, 175 with two coats. Coverage by surface, a gallons chart by room size and a quick formula.
- How Much Paint to Paint the Outside of a House (Size Chart)A 40 × 30 ft one-story house takes about 7.4 gallons for two coats; a two-story one takes 13.7. Gallons by house size and siding type.
- How Many Rolls of Wallpaper Do I Need? Single and Double Rolls by RoomA room with 40 ft of wall, 8 ft ceilings and 40 sq ft of openings needs 12 single rolls (6 double rolls) with 15% waste. Charts by room size and pattern repeat.
- How Many Tubes of Caulk Do I Need? Feet per Tube by Bead SizeA standard 10.1 oz tube of caulk fills about 24 feet of a 1/4 × 1/4 inch joint. A chart of feet per tube by bead size, and the tubes for 40 and 100 feet.
- How Much Deck Stain Do I Need? Gallons by Deck Size and CoverageA 12 × 16 ft deck needs about 1 gallon of stain for one coat at 200 sq ft per gallon, 2 gallons for two coats. Charts by deck size and coverage, with railings.
- Paint Sheen Guide: Flat, Eggshell, Satin or Semi-Gloss?Which paint finish to use in each room: flat, eggshell, satin or semi-gloss, how sheen affects wipe-ability and flaws, and how much paint a room needs.
- Exterior House Painting Materials List: Paint, Primer and PrepWhat to buy to paint the outside of a 40×30 ft one-story house: paint, primer, caulk, tape and prep supplies, with a size chart and a lead-paint warning.
- Painting a Room Materials List: Paint, Primer, Tape and SuppliesWhat to buy to paint a 12×14 ft bedroom: wall and ceiling paint, primer, tape, caulk and supplies for a clean job, with a chart for other rooms.
- How Much Paint Do I Need? Gallons by Room Size ChartWork out how much paint to buy for walls and ceilings: the formula, coverage per gallon, how many coats, and a chart of common room sizes.
Other guides that use these calculators: Common Mistakes When Building a Deck (Boards, Joists, Gaps) · How Many Deck Screws Do I Need? Chart by Deck Size · How Much Baseboard and Trim Do I Need? Boards by Room Size · How Much Crown Molding Do I Need? Feet, Pieces and Corners · How Much Shiplap Do I Need? Boards and Linear Feet · Wood vs Composite Decking: Which Should You Choose? · Board and Batten Spacing: How to Lay Out an Accent Wall · Deck Materials List: Boards, Joists and Screws for a 12×16 Deck · Privacy Fence Materials List: Posts, Rails, Pickets and Concrete · Drywall Materials List: Sheets, Screws, Tape and Joint Compound
Answers for common sizes
Already know the size? These pages give the worked answer for one common size each, with the inputs filled in so you can adjust them.
Project planners
Planning the whole job rather than one material? These step-by-step planners put the calculators above in the order you will need them.
Frequently asked questions
How many square feet does a gallon of paint cover?
Around 350 to 400 square feet per coat on smooth, primed walls. Rough, porous or new surfaces take more; the label on the can is the figure to trust.
How much paint for a 12 x 12 room?
About 1.9 gallons for two coats on the walls with 8 ft ceilings, one door and two windows. Buy whole gallons.
Do I need two coats of paint?
Usually yes. One coat rarely hides the old color evenly, and two coats wear better. A primer coat comes first on new drywall or patched areas.
Should the ceiling be painted first?
Yes. Paint the ceiling, then the walls, then the trim, so drips and roller spatter only ever land on surfaces you have not painted yet.
Related topics
Estimates only. Quantities depend on your materials, site and supplier, so check coverage and sizes on the label. Follow local building codes for anything structural. How we calculate.