Paint Calculator
Calculate how much paint you need for a room. Enter dimensions, doors, and windows to get liters and cans needed.
Key features
- Room dimension input
- Door/window deduction
- Coverage calculation
- Can size estimation
Guide
Calculating how much paint you need before starting a project saves money, prevents waste, and eliminates mid-project trips to the store. The mathematics behind paint calculation are straightforward: measure the surfaces, subtract areas you will not paint, account for coverage rates and number of coats, then add a margin for waste. This guide covers the complete process for interior and exterior rooms of any shape. Start by measuring each wall. For a rectangular wall, multiply the width by the height to get the area in square feet or square meters. A wall that is 12 feet wide and 8 feet tall has an area of 96 square feet. Measure every wall in the room, including small sections, alcoves, and bump-outs. Write down each measurement as you go. Relying on memory leads to errors, and measuring twice is faster than making a return trip to the paint store. Standard room height in most homes is 8 feet (2.44 meters) in the United States, though older homes and some newer construction may have 9-foot or 10-foot ceilings. Measure your actual ceiling height rather than assuming. Even a 6-inch difference across four walls of a medium room changes the total area by several square feet. In homes with crown molding, measure to where the wall paint stops, not to the ceiling. Subtract areas that will not be painted. A standard interior door is approximately 20 square feet (roughly 3 feet by 6 feet 8 inches). A standard window averages about 15 square feet, though sizes vary widely. Measure each window and door to get accurate numbers, or use these averages for a quick estimate. Subtract the total non-painted area from the total wall area. If your four walls add up to 400 square feet and you have two doors (40 square feet) and three windows (45 square feet), your paintable area is 315 square feet. Also subtract areas covered by built-in bookcases, fireplaces with stone or brick surrounds, and any other permanent fixtures that extend from floor to ceiling. Paint coverage rate is listed on every can. Most interior latex paints cover 350 to 400 square feet per gallon on smooth surfaces. Premium paints sometimes cover up to 400 square feet. Budget paints may cover only 300 square feet. Textured surfaces like stucco, brick, or heavily textured drywall absorb more paint and reduce coverage to 200 to 300 square feet per gallon. Always check the coverage rate on your specific paint product rather than guessing. The number of coats depends on several factors. Going from a lighter color to a darker color usually requires two coats. Going from a darker color to a lighter one often requires three coats or a coat of primer plus two topcoats. Painting over a similar color might need only one coat, but two is standard practice for uniform coverage and durability. Most paint professionals apply two coats as a default. Using a tinted primer that matches the finish color direction can reduce the number of topcoats needed when making dramatic color changes. For example, when painting a white wall dark navy blue, a gray-tinted primer gets you closer to the final color and prevents the white from showing through. The basic formula is: gallons needed = (paintable area times number of coats) divided by coverage rate per gallon. For a room with 315 square feet of paintable area, two coats, and paint that covers 350 square feet per gallon: (315 times 2) divided by 350 equals 1.8 gallons. Round up to 2 gallons. Add 10 to 15 percent for waste, touch-ups, and areas where extra paint soaks in (corners, edges, spots where you cut in with a brush). That 1.8 gallons becomes roughly 2.07, which you would round to 2 gallons for a straightforward room or consider buying a third gallon if you want extra for future touch-ups. Rollers absorb paint that cannot be fully recovered. Brush work along edges and corners uses more paint per square foot than roller application on flat surfaces. Both contribute to waste above the theoretical coverage rate. Paint is sold in quarts (0.25 gallon), gallons, and 5-gallon buckets. For small rooms or accent walls, a quart or two might suffice. For large rooms or multiple rooms in the same color, a 5-gallon bucket is more economical per unit and ensures color consistency across all surfaces. Mixing paint from two different gallons can produce slight color variations, especially with custom-mixed colors. A single 5-gallon bucket eliminates this risk. Paint samples (typically 8 ounces) cover about 75 square feet with one coat, enough to test a 4-by-4-foot section of wall to evaluate the color before committing. Primer requirements follow the same area calculation but with a different coverage rate. Primer typically covers 300 to 400 square feet per gallon. You need primer when painting over bare drywall, wood, patched areas, or stained surfaces. Primer is also necessary when switching from oil-based to latex paint or when making dramatic color changes. Some modern paints include primer (paint and primer in one), which can reduce total application steps but does not eliminate the need for dedicated primer on bare surfaces. Primer also blocks stains from water damage, smoke, or markers from bleeding through the finish coat. Ceiling paint calculation uses length times width for the room's ceiling area. A 12-by-14-foot room has 168 square feet of ceiling area. Standard white ceiling paint covers about 350 to 400 square feet per gallon. Ceilings usually need one coat if previously painted white. Textured ceilings (popcorn ceilings) absorb more paint and may need two coats. Subtract ceiling-mounted fixtures, skylights, or other non-painted areas. Ceiling paint is formulated to be thicker than wall paint to reduce dripping, and it typically has a flat finish to hide imperfections. Trim, doors, and baseboards have their own paint requirements. Trim is typically painted with a different finish (semi-gloss or high-gloss for durability and cleanability) than walls (flat or eggshell). To estimate trim paint: measure the linear feet of baseboard and multiply by the baseboard height (usually 3 to 6 inches). For door frames and window trim, estimate the linear footage and width. A standard interior door (both sides) requires about 1.5 to 2 quarts including the frame. Trim areas add up to less paint than walls. A quart covers roughly 75 to 100 square feet, which is enough for the trim in most individual rooms. Surface preparation affects how much paint you actually use. Smooth, primed surfaces require the least paint. Surfaces with patches or repairs where joint compound was applied absorb more paint in those spots, which is why a primer coat over patched areas is important before applying finish paint. Sanding between coats on trim and high-gloss surfaces improves adhesion but does not significantly change paint consumption. Cleaning walls with a damp cloth before painting removes dust and grease that can prevent proper adhesion and cause the paint to require an additional coat. Paint sheen matters for coverage and appearance. Flat and matte finishes hide wall imperfections best but are harder to clean. Eggshell and satin finishes offer a slight sheen and are easier to wipe down, making them popular for living rooms and bedrooms. Semi-gloss and high-gloss finishes are the most durable and cleanable but highlight every wall imperfection. Higher-sheen paints tend to cover slightly less area per gallon because the reflective additives change the paint consistency. Kitchens and bathrooms benefit from semi-gloss because it resists moisture and is easy to clean. Room shapes that are not simple rectangles require breaking the space into manageable sections. An L-shaped room is two rectangles. A room with a bay window has angled walls that you measure individually. A room with a vaulted ceiling has triangular wall sections above the standard wall height. For triangular areas, multiply the base by the height and divide by 2. Measure each section, calculate its area, and sum them all. For arched windows or doorways, estimate the arch area as roughly half the area of a circle with the arch's width as the diameter. Bathroom and kitchen calculations should account for areas covered by tile backsplash, shower surrounds, tub enclosures, and large built-in cabinets. Subtract these areas just as you would subtract windows and doors. Bathrooms and kitchens also benefit from moisture-resistant paint (kitchen and bath formulations) that may have slightly different coverage rates. These specialty paints contain additives that resist mildew growth in high-humidity environments. Exterior paint calculation follows similar principles but with important differences. Exterior surfaces often include siding, trim, soffits, fascia, shutters, doors, and porch ceilings. Measure each surface type separately because different surfaces may require different paint types. Exterior paint typically covers 250 to 400 square feet per gallon depending on the surface material. Wood siding absorbs more than vinyl or aluminum. Bare wood may need primer plus two coats. Previously painted surfaces in good condition may need only one coat. Multiple rooms in the same color benefit from buying all the paint at once and requesting the store to batch-mix it. Small batch variations in custom colors are normal. Having all your paint from the same batch ensures consistent color throughout your home. Calculate the total area across all rooms, then divide by the coverage rate. For a whole-house paint job, the 5-gallon bucket becomes the standard purchase unit. Temperature and humidity affect drying time and coverage. Paint applied in very hot conditions (above 85 degrees Fahrenheit) dries too fast, leading to visible brush or roller marks and potentially poor coverage. Paint applied in cold conditions (below 50 degrees for latex) may not cure properly. Ideal conditions are 50 to 85 degrees Fahrenheit with moderate humidity. These conditions do not change how much paint you buy, but they affect how well each coat covers. High humidity above 85% can cause latex paint to sag and run, requiring more paint for corrections. The cost of paint varies widely. Budget interior paint runs $20 to $30 per gallon. Mid-range paint costs $30 to $50 per gallon. Premium paint from top brands costs $50 to $80 or more per gallon. The price difference reflects coverage quality, durability, washability, and color accuracy. One coat of premium paint at $60 per gallon may deliver better results than two coats of budget paint at $25 per gallon, and you use less total paint. Calculate the total cost including the number of coats needed, not just the per-gallon price. Tools affect paint consumption. Roller nap length (the thickness of the roller cover fabric) determines how much paint the roller holds and how it applies. Smooth surfaces use 3/8-inch nap rollers. Lightly textured surfaces use 1/2-inch nap. Heavily textured surfaces use 3/4-inch or thicker nap. The wrong roller nap wastes paint and produces poor results. Paint trays and bucket grids also affect how efficiently you load the roller. Keep leftover paint for touch-ups. Store it in a sealed container (the original can with the lid hammered tight, or transfer to a smaller container with less air space). Label the container with the room it was used in, the color name, the color code or formula, and the date. Properly stored latex paint lasts 2 to 10 years. Having touch-up paint available saves you from repainting an entire wall when furniture scratches the surface or a picture hanging goes wrong. Take a photo of the paint can label with the formula on it in case you need to reorder the exact color in the future. The WebRecast paint calculator takes your room dimensions, number of doors and windows, number of coats, and paint coverage rate, then outputs the total paint needed in gallons and liters. It handles the math instantly so you can focus on choosing colors and finishes rather than crunching numbers with a calculator. Accent walls require a separate calculation. An accent wall is a single wall painted a different color for visual contrast. Calculate its area independently and buy that color separately. A typical accent wall in a 12-by-14-foot room is about 112 square feet (14 feet wide times 8 feet tall), which requires about 1 gallon with two coats. The remaining three walls total about 288 square feet and need their own color. Stairwells and two-story foyers present measurement challenges because of height. A stairwell wall may be 16 to 20 feet tall. Calculate these tall walls using the full height. Painting them requires extension ladders or scaffolding, and the difficulty of reaching high areas means you should add extra waste margin (15 to 20% instead of the standard 10%). The awkward angles where stairwell walls meet ceilings also consume more paint during cutting-in. Wainscoting and chair rails split a wall into two zones. Below the chair rail (wainscoting area) may use a different color or finish than above. Measure each zone separately. The wainscoting area is typically 32 to 36 inches from the floor. Multiply the room perimeter by the wainscoting height for the lower zone area, and by the remaining height for the upper zone area. Subtract doors and windows from whichever zone they fall in. Paint type affects both coverage and durability. Latex (water-based) paint is the most common for interior walls. It dries quickly (1 to 2 hours between coats), cleans up with water, has low odor, and maintains color flexibility well. Oil-based (alkyd) paint offers superior adhesion, smoother finish on trim, and better stain blocking, but it requires mineral spirits for cleanup, has strong fumes, takes 8 to 24 hours between coats, and yellows over time on light colors. Hybrid (alkyd modified latex) paints combine some benefits of both types. Cabinet paint formulations are designed for kitchen cabinets and provide a hard, durable finish that resists chipping. A gallon of paint covers approximately 350 to 400 square feet. A quart covers 87 to 100 square feet. A sample pot (8 ounces) covers about 50 to 75 square feet. These numbers assume smooth, previously painted surfaces with one coat. Reduce coverage expectations by 20 to 30% for rough or porous surfaces. Increase by 10% for high-quality paint with superior hiding power. The coverage number on the can is the manufacturer's estimate under ideal conditions. Color theory affects how many coats you need. Changing color families (warm to cool, or the reverse) requires more coats than staying within the same family. Red and orange pigments are notoriously transparent and often need 3 to 4 coats over a white base. Dark colors over light backgrounds need a tinted primer that bridges the gap. Gray primers work well under most medium-to-dark colors. White primers are best under light colors. Using the right primer base reduces topcoat needs by 1 to 2 coats, which can save an entire gallon on a large room. Estimating paint for the entire house at once lets you plan a bulk purchase and potentially negotiate a contractor discount. Add up every room, hallway, closet, and common area. A typical 2,000-square-foot home has roughly 5,000 to 6,000 square feet of wall surface (due to the height multiplier), minus about 1,000 square feet for windows, doors, and non-paintable areas. The net paintable area is about 4,000 to 5,000 square feet, requiring 10 to 15 gallons for two coats. Add 2 to 3 gallons for trim, 2 to 3 gallons for ceilings, and extra for waste and touch-ups. A total house paint job typically requires 15 to 25 gallons depending on home size and complexity. For the most accurate results, measure your actual room rather than relying on floor plans or real estate listings. Floor plans show interior dimensions that may not account for molding, built-ins, or irregular wall surfaces. A tape measure and five minutes of measuring give you numbers you can trust. Write them down, enter them into the calculator, and buy paint with confidence that you have enough to finish the job without waste.
Frequently asked questions
What coverage is assumed?
Standard coverage of 10-12 square meters per liter.
