Free paint needed calculator. Enter room dimensions, doors, windows, coats and price per gallon to get gallons, liters, cans to buy and the total paint cost estimate.
Your results will appear here.
Enter your values and press Calculate.
The calculator finds the total wall area from your room dimensions (perimeter times ceiling height), subtracts a standard 21 sq ft for each door and 15 sq ft for each window, and adds the ceiling area if you select it. It multiplies the net area by your number of coats and divides by the coverage rate printed on your paint can to get exact gallons, then adds your waste allowance and rounds up to whole cans. Cost is cans times your price per gallon. This is a planning estimate to help you shop: real usage varies with surface texture, application method and how much the old color shows through. The waste factor you enter covers spills, roller absorption, cut-ins and touch-up paint kept for later repairs.
Every paint estimate is built from four numbers: the net paintable area, the number of coats, the coverage rate per gallon, and a waste allowance. Wall area is 2 times (length plus width) times ceiling height. A standard interior door removes about 21 sq ft and a standard window about 15 sq ft. Exact gallons equals (net area times coats) divided by coverage per gallon, and because paint is sold in whole cans, the cans-to-buy figure rounds the waste-adjusted total up.
Worked example 1: a 12 by 12 ft room with 8 ft ceilings, 1 door and 2 windows. Wall area is 384 sq ft, openings remove 51 sq ft, leaving 333 sq ft net. Two coats at 350 sq ft per gallon gives 1.90 gallons exact, 2.09 gallons after a 10% waste allowance, so you buy 3 one-gallon cans (7.9 liters). At $40 a gallon the paint cost is $120, about $0.36 per sq ft.
Worked example 2: a 15 by 18 ft room with 9 ft ceilings, ceiling included, 2 doors and 4 windows, two coats on textured walls at 300 sq ft per gallon with 15% waste. Wall area is 594 sq ft, openings remove 102 sq ft, plus a 270 sq ft ceiling gives 762 sq ft paintable. That is 5.08 gallons exact, 5.84 gallons with waste, so buy 6 cans (22.1 liters). At $55 a gallon the estimate is $330.
This paint quantity calculator and estimator treats primer as a separate purchase, because primer has its own coverage rate and its own cost per square foot.
Enter your room length, width and ceiling height in feet, then the number of doors and windows. Choose whether to include ceiling paint, set your number of coats (2 is the industry standard), and type the coverage rate from your paint can, 350 sq ft per gallon is a safe default for smooth interior walls. Add a waste allowance (10% is typical) and your price per gallon in your currency.
Click Calculate to see your net paintable area, exact gallons, gallons with the waste allowance, the liter equivalent, the number of 1-gallon cans to buy, and the estimated paint cost with cost per sq ft. If you are painting several rooms, run each room separately and add the can counts together, then consider 5-gallon buckets for the bulk of it.
These quick figures assume 8 ft ceilings, 2 coats, smooth primed walls, one door and two windows, at 350 sq ft per gallon. Use the calculator above for your exact room.
Small bathroom (5 by 7 ft): about 171 sq ft net, roughly 1 gallon, buy 1 can. Standard bedroom (10 by 12 ft): about 316 sq ft net, 1.81 gallons, buy 2 cans. Larger bedroom (12 by 14 ft): about 432 sq ft net at 9 ft ceilings, 2.47 gallons, buy 3 cans. Living room (15 by 18 ft): about 543 sq ft net, 3.10 gallons, buy 4 cans. Garage or basement (20 by 20 ft at 10 ft ceilings): about 764 sq ft net, 4.37 gallons, buy 5 cans.
An accent wall alone is far less: a 12 by 8 ft accent wall is 96 sq ft, so 0.55 gallons for 2 coats, one can is plenty with touch-up paint left over. A whole-house interior repaint of around 2,000 sq ft typically needs 11 to 12 gallons for two coats.
Coverage per gallon tells you how many square feet one gallon covers with one coat on a smooth, previously painted wall. Typical published rates are 350 to 400 sq ft per gallon for standard latex, 400 to 450 for premium lines, and 300 to 350 for primer. Always check the specific can rather than relying on the generic 350 rule, because brand, sheen and tint depth all shift the number.
Surface texture changes everything: heavily textured walls drop coverage to roughly 250 to 300 sq ft per gallon, and new unprimed drywall can soak up 40 to 50 percent more paint than a smooth primed wall. Exterior surfaces are even thirstier: rough stucco or brick can drop to 150 to 250 sq ft per gallon. If your walls are textured or you are painting bare drywall, enter the lower coverage number your paint data sheet suggests instead of the default.
You do not paint glass or door slabs, so subtract about 21 sq ft per standard door and 15 sq ft per standard window. In a room with one door and two windows that is 51 sq ft, roughly 0.15 gallons per coat saved, and over a whole house the deductions add up to real money.
Ceilings are calculated separately: ceiling area is simply room length times room width. A 12 by 14 ft ceiling is 168 sq ft, about half a gallon for two coats. Buy ceiling-specific paint, not your wall paint: it has a flat finish that hides imperfections and an anti-drip formula for overhead work. Trim, baseboards and crown molding use semi-gloss or high-gloss paint and should be estimated as their own purchase, not blended into the wall gallons.
Primer is a separate product with its own math, not an extra coat of your finish paint. You need primer for new drywall, for a dark-to-light color change, for stained or patched areas, for bare wood, and when switching between oil and latex paint. Primer covers about 300 to 400 sq ft per gallon and counts as one dedicated coat.
Sheen affects appearance and durability, not the gallon math. Flat or matte hides imperfections and suits low-traffic bedrooms and ceilings. Eggshell is the standard for living rooms and hallways. Satin and semi-gloss resist moisture and scuffing, making them right for kitchens, bathrooms, trim, doors and baseboards.
Latex (water-based) paint is the right choice for most interior walls: it dries fast, has low odor and cleans up with soap and water. Oil-based paint is now mostly reserved for high-durability trim and cabinetry. Both follow the same coverage math, but oil-based products often list slightly lower coverage, so check the label.
This quick sheen guide covers the common choices: flat for ceilings and low-traffic bedrooms, eggshell for living areas, satin or semi-gloss for kitchens, baths and trim.
Exterior paint uses the same formula but rougher assumptions. Measure the house perimeter times wall height, subtract doors, windows and garage doors, and use a lower coverage rate, 250 to 350 sq ft per gallon for smooth siding, down to 150 to 250 for rough stucco or brick. Most exterior jobs need 2 coats of topcoat plus a primer coat. A typical house exterior needs 8 to 15 gallons for two coats.
Exterior tips from professional painters: use 100% acrylic paint for durability, paint in 50 to 85 degree weather, follow the shade around the house instead of painting in direct sun, and power wash before you start. For the calculator on this page, enter your exterior wall rectangle as the room dimensions (perimeter as length, height as ceiling height) and set doors and windows to your totals.
Buy paint during holiday sales, when 30 to 40 percent off is common. For projects over 5 gallons, 5-gallon buckets cost 5 to 10 percent less per gallon than single gallons. Quality rollers give better coverage than cheap ones, and one gallon of premium paint can outperform two gallons of budget paint on hiding power.
If a project needs more than one gallon of the same color, box the cans: pour them all into one large bucket and mix. Even paint from the same store can vary slightly between cans, and boxing guarantees color consistency. Buy all the paint from the same batch or store visit for the same reason. Keep at least one quart of each color in a sealed, labeled container indoors for touch-ups, not in the garage, and save your receipt in case you need a bit more.
For a 12 by 12 ft room with 8 ft ceilings, one door and two windows, the net wall area is about 334 sq ft after subtracting openings. At 350 sq ft per gallon that is roughly 1.8 gallons for two coats, so buy 2 one-gallon cans. Add one more gallon if you are also painting the ceiling. The 12x12 room is the classic benchmark size painters quote against.
One gallon covers about 350 to 400 sq ft per coat on smooth, primed walls. Coverage drops to 250 to 300 sq ft on textured surfaces, 300 to 350 for primer, and 150 to 250 on rough exterior surfaces like brick or stucco. Always check the specific paint can label, since coverage varies by brand, sheen and tint.
Two coats is the industry standard. One coat rarely provides full coverage: the old color bleeds through and the finish looks uneven. When painting a lighter color over a darker one, plan for three coats or a tinted primer first. A fresh coat of the same color on already-painted walls is the one case where a single coat can suffice.
Yes. A standard door is about 21 sq ft and a standard window about 15 sq ft. In a room with one door and two windows that is 51 sq ft subtracted, saving roughly 0.15 gallons per coat. This calculator applies the deduction automatically from your door and window counts.
DIY paint alone runs about $60 to $110 for a 12 by 12 ft room at $30 to $55 per gallon, plus $40 to $80 for supplies like rollers, tape and drop cloths. Professional labor adds $300 to $800 per room depending on region and prep work. Enter your price per gallon above for an estimate based on your exact room.
Yes for new drywall, dark-to-light color changes, stained or patched areas, bare wood, or switching between oil and latex paint. Paint-plus-primer combos only work for same-color touch-ups and light repaints. Primer is a separate product with coverage of roughly 300 to 400 sq ft per gallon, calculated as its own coat.
Yes. Ceiling paint has a flat finish that hides imperfections and is formulated to drip less during overhead application. Ceiling area is simply room length times room width. Toggle the ceiling option in the calculator above and it adds the ceiling area into your gallon estimate, but buy the ceiling paint as a separate product.
Flat or matte suits low-traffic bedrooms and ceilings because it hides imperfections. Eggshell is the most common choice for living rooms and hallways. Satin or semi-gloss is best for kitchens, bathrooms, trim and doors because it resists moisture and wipes clean easily. Sheen does not change the gallon math.
Keep at least one quart of each color in a sealed, labeled container stored indoors. The calculator's waste allowance (default 10%) plus the round-up to whole cans usually leaves exactly this buffer. Future touch-ups from the same batch blend perfectly; matching a color months later almost never does.
Yes, significantly. Heavily textured walls reduce coverage by roughly 20 to 30 percent, and new unprimed drywall can absorb 40 to 50 percent more paint than a smooth primed wall. Always prime new drywall first, and enter a lower coverage rate (250 to 300 sq ft per gallon) in the calculator for textured walls.
Latex paint needs about 2 to 4 hours of dry time between coats, and oil-based paint needs about 24 hours. Full curing takes 14 to 30 days depending on paint type and conditions. Ideal painting conditions are 50 to 85 degrees with humidity below 85 percent, since temperature and humidity strongly affect drying.
Use latex (water-based) for most interior walls: it dries fast, has low odor, cleans up with soap and water and stays flexible so it resists cracking. Reserve oil-based paint for high-durability trim, doors and cabinetry, where its harder, glossier finish pays off. Both follow the same coverage math, but check the can label since oil-based products often list slightly lower coverage.
Find out exactly how many wallpaper rolls your walls need.
Find exactly how many tiles, boxes, and dollars your floor or wall project needs.
Gallons, liters, and primer for any paint job.
Find how many gallons of paint you need and the true cost of painting any room.