How Many Weeds Will One Gallon of Roundup Kill?

Roundup Weed and Grass Killer III

• Although Roundup has many formulations for a variety of uses, the standard formula is Weed and Grass Killer III. The label on the 1.33 gallon Pump ‘N Go carton states the “container treats more than 1,400 weeds” in an area “up to 400 square feet.” To find the multiplier for 1 gallon, divide 1.33 by four and multiply by three to get about 1 gallon. This gives a multiplier of 75 percent. To find the number of weeds treated with 1 gallon, multiply 1,400 by 75 percent, which equals 1,050 weeds. Find square footage treated by 1 gallon by multiplying 400 square feet by 75 percent, which equals 300 square feet. One gallon will treat about 1,100 weeds or roughly 300 square feet.

Roundup Concentrate Plus

• Some Roundup formulas, like Roundup Concentrate Plus, require mixing. To make one gallon, mix 3/4 cup of Roundup Concentrate Plus and 1 gallon of water. This will treat about 300 square feet. According to the Scotts Company, you can approximate the number of weeds treated by comparing that 1 gallon of Roundup Weed and Grass Killer III kills about 1,100 weeds in a 300 square feet area. Since one gallon of Roundup Concentrate Plus mix treats 300 square feet, when applied evenly, 1 gallon would treat about 1,100 weeds.

Roundup Super Concentrate

• The highest concentrated herbicide made by Scotts is Roundup Super Concentrate. It is more than 50 percent glyphosate. Mix 5 tablespoons with a gallon of water to make 1 gallon of herbicide that will treat 300 square feet. This formula also treats approximately 1,100 weeds in 300 square feet, the same as 1 gallon of Roundup Concentrate Plus. The formula can be mixed at a lower concentration but will still treat the same number of weeds and square footage.

Poison Ivy Plus

• Roundup Ready-to-Use Poison Ivy Plus Tough Brush Killer comes in a 1.33 gallon container and treats about 400 square feet. This formula is used to treat grasses, woody vines and weeds. Based on the formula given by the Scotts Company, this product will kill about 1,100 weeds in a 300 square feet area. However, because areas with woody vines may not contain as many weeds as areas with dense weeds and no woody vines, that number may be lower. The amount of product sprayed would be at least as much, because vines are usually longer than weeds are tall. Keep in mind the number is an approximation.