Paint Cost Calculator

How much paint a room needs

Paint math is area divided by coverage, and the area is the four walls minus the doors and windows you are not painting. The calculator above walks the whole thing: room size, wall height, openings, coats, coverage and price, and it returns the gallons to buy and the total cost.

• Wall area = 2 x (length + width) x ceiling height.
• Openings = 20 square feet per door and 15 square feet per window, the standard estimates.
• Ceiling = length x width, if you are painting it.
• Coats = 2 in almost every case.
• Gallons = total square feet x coats / coverage per gallon, then round up.

Coverage is the number people get wrong. A can usually states 350 to 400 square feet per gallon on smooth, primed drywall, but textured walls, bare drywall and deep colors can drop that to 250. When in doubt, use 350 for the estimate and check the can before you buy. The EPA lead-safe renovation program is worth reading before you disturb paint in a home built before 1978, because old paint can contain lead.

Worked example: a 12 by 12 bedroom

Take a 12 foot by 12 foot bedroom with 8 foot ceilings, two doors and two windows, painted in two coats of a mid-range paint at $35 a gallon.

• Wall area: 2 x (12 + 12) x 8 = 384 sq ft
• Openings: 2 doors x 20 + 2 windows x 15 = 70 sq ft
• Paintable wall: 384 - 70 = 314 sq ft
• Two coats: 314 x 2 = 628 sq ft
• Gallons: 628 / 350 = 1.79, so buy 2 gallons
• Cost: 2 x $35 = $70

That is $70 in wall paint. Add the ceiling at 144 square feet for one coat, 144 / 350 = 0.41 gallon, so a quart covers it and you are at about $85 to $90 total. Add a gallon of primer at $25 if the walls are bare or freshly patched, and the materials land near $115.

Now change the surface. If the walls are textured, coverage drops to about 250 square feet per gallon, and the same 628 square feet needs 2.51 gallons, so 3 gallons and $105 instead of $70. That is a 50 percent jump from texture alone, and it is why the coverage figure matters as much as the room size.

Worked example: an open living area with a ceiling

A bigger space shows how gallons add up. Say a living room is 20 feet by 16 feet with 9 foot ceilings, one wide doorway and four windows, painted in two coats, ceiling included.

• Wall area: 2 x (20 + 16) x 9 = 648 sq ft
• Openings: 1 doorway x 20 + 4 windows x 15 = 80 sq ft
• Paintable wall: 648 - 80 = 568 sq ft
• Two coats: 568 x 2 = 1,136 sq ft
• Wall gallons: 1,136 / 350 = 3.25, so buy 4 gallons
• Ceiling: 20 x 16 = 320 sq ft, one coat = 0.91 gallon, buy 1

So the walls take 4 gallons and the ceiling 1, five gallons in total. At $35 a gallon that is $175 in paint, and the ceiling paint is often cheaper, so call it $165. If you also paint the trim, add about 0.5 gallon of a durable trim paint, another $20 to $30.

The living area costs 2.5 times the bedroom in paint for roughly 1.9 times the floor area, because the taller ceiling adds wall area faster than the floor grows. Ceiling height is the quiet multiplier in paint estimates, and it is the figure people leave out when they eyeball a room.

Paint coverage and cost at a glance

Coverage drives the gallon count, and the gallon count drives the cost. These are realistic single-coat coverage figures for common surfaces.

Two rules of thumb fall out of this table. First, bare drywall always needs more paint than a repaint, because the first coat soaks in, so budget an extra 15 to 20 percent. Second, cheap paint is rarely the cheaper job, because a paint with better coverage and hiding can do in two coats what a thin one does in three. Compare price per square foot of coverage, not price per can.

Primer, trim and the extras people forget

The paint itself is usually less than half the cost of a paint job. The rest is supplies, and skipping them shows up as a poor finish or a second trip to the store.

• Primer: needed on bare drywall, patched spots, and any dark-to-light color change. One gallon covers about 350 square feet.
• Tape and plastic: painter's tape for trim and a drop cloth for the floor, about $15 to $25.
• Rollers and trays: a quality roller and a good tray, about $15, and they outlast the cheap ones by a wide margin.
• Brushes: one angled brush for cutting in, about $10 to $15.
• Sandpaper and filler: for patching nail holes and dings before you paint, a few dollars.
• Trim paint: a separate, harder finish for baseboards and door casings, often $30 to $50 a gallon.

A 12 by 12 room typically runs $50 to $80 in supplies on top of the paint. That is the difference between a $70 paint bill and a $130 to $150 project, which is why a paint cost calculator should report materials, not just gallons. The Ohio State University Extension publishes home-maintenance guides that cover prep and painting in plain language.

Buying paint without leftovers or second trips

The goal is to finish the job with a little paint left over, not a lot and not none. A few habits get you there.

• Round up to the nearest gallon, then add one quart. The quart covers touch-ups and the odds that a wall drinks more than expected.
• Buy all the paint at once. Different batches can differ slightly in color, so mixing gallons from two trips risks a visible seam.
• Keep the label. Write the room, the color code and the date on the lid so a future match is easy.
• Store it right. Seal the can, keep it indoors, and it will keep for years. Freezing ruins latex paint.
• Recoat on time. Latex needs 2 to 4 hours between coats and about 30 days to cure, so do not rush the second coat or wash the wall early.

If you are weighing a contractor against doing it yourself, materials are the smaller number. Professional interior painting runs $2 to $6 per square foot of floor area, so a 12 by 12 room is roughly $300 to $800 installed against about $130 in materials. The math here is for materials only, and it is an estimate for planning. All of the calculations run in your browser, and nothing you type is uploaded.