How Much Paint Will A Gallon of Hand Applied or Sprayed Paint Cover

If you are involved with painting whether it be as a contractor, home owner, or production shop employee it will be critical to know how many square feet you can expect out of a gallon of paint. This will allow you to properly bid your material cost for your jobs. Below we will cover how many square feet a gallon of paint will cover.

Coverage will depend on application method

Essentially there are multiple ways coating is applied including Spray Guns, Airless Paint Sprayers, Electrostatic spray Equipment, or hand applied. Each one of these methods will yield a different rate of coverage and have different benefits and drawbacks. For a good overview of spray guns this article covers their differences and benefits as well as drawbacks. For an overview of airless application equipment vs spray guns this article provides a good overview. Finally if you want to learn about Electrostatic this article provides a good overview. The reason for differing coverage rates is due to the efficiency that coating is transferred to your product.

Overview of Transfer Efficiency of Different Application Methods from highest to lowest

• Hand Applied – 100% efficient though much slower than spray applications
• Electrostatic Spray Gun – Transfer Efficiency Between 85- 95% efficient
• HVLP Spray Gun – Around 65% efficient
• Airless Paint Sprayer/ Conventional Spray Gun- 35-40% efficient

Math To Determine Coverage Will Depend on Type of Painting Being Done

For Painting a building, home, or office by hand you can use this calculator below or if you have your technical data sheet this article has a calculator to determine how much paint you would use spraying vs hand applying any coating.

• It is assumed coating is being applied by hand in the following formula. If you are spraying the coating you would take the 350 square feet * the efficiency of your equipment to have a rough estimate of coating needed
• Coverage for architectural coatings is typically 350 Sq Feet per Gallon. This means if you are estimating coating for a home you will take the square footage of the room by multiplying the length of all the walls by their height. Then subtract the (width x height) of the windows and doors to give you the total surface to be painted. Take the square footage and divide by 350 to give you the approximate gallons needed. Remember this is for a single coat and will need additional paint for additional coats. Lets take a quick example: You have a family room that has 4 walls and a ceiling with two windows that are 2 feet wide by 3 feet tall. The room is 20 feet long by 10 feet wide with 8 feet high walls. Here is the math for the square feet of the room.

Length of walls – 20 + 20 +10 + 10 = 60

Multiply wall length by room height = 60 * 8 = 480

Find windows square feet by taking height x width x number of windows (or individually if different sizes) = 2 x 3 x 2 = 12

Subtract windows from room square feet = 480 – 12 = 468

Divide room square feet by coverage for a gallon of paint = 468/ 350 = 1.33 gallons

If above .5 gallons get an extra gallon of paint if less each quart is equal to .25 gallons so buy appropriate number of quarts (2 quarts in this problem)

Remember the 350 square feet is an approximate number and is dependent on factors including if the drywall is new (which will absorb more paint), if it is a rough textured surface which will absorb more paint, as well as how thick the paint is applied, typically its best to err on the side of caution when estimating the amount of paint.

For Painting with a Spray Gun or Airless Paint Sprayer using Architectural Coatings, Industrial, Wood, and Auto Body Coatings

Unlike hand painting, applying a coating with a spray gun will require different math. The factors involved with industrial, wood, and auto body coatings include percent solids of the coating, the mil thickness required, and the transfer efficiency of your painting equipment. 

• Take the theoretical coverage rate from your paint manufacturer technical data sheet and enter into B4
• Take transfer efficiency percent in decimal form and enter into B5 (see above)
• Enter the percent of solvent in decimal form added to the coating

The number provided will be the amount of coating you can expect to get out of spraying.

As you can see spraying is not nearly as efficient as hand application but it is faster and can yield a better finish. Additionally, it will depend heavily on the transfer efficiency you can achieve. Of the factors you can control transfer efficiency is the only variable that can be improved by using proper technique and equipment.

Photo by YoctoArts (YoctoArts) [GFDL or CC BY-SA 4.0-3.0-2.5-2.0-1.0], via Wikimedia Commons