For Roundup Weed & Grass Killer Concentrate Plus, mix from 3 ounces, or 6 tablespoons, to 6 ounces, or 12 tablespoons, concentrate with 1 gallon of water. For Roundup Weed & Grass Killer Super Concentrate, use from 1 1/2 ounces, or 3 tablespoons, to 2 1/2 ounces, or 5 tablespoons, per 1 gallon of water.Click to see full answer. Consequently, how much Roundup do I need for 20 gallons of water?You really have to read the container label. The Round-up super concentrate label says 2.5 ounces per gallon of water so for 20 gallons, you would need 50 ounces or 6.25 cups.One may also ask, how much Roundup do I need for a 4 gallon sprayer? Roundup Pro Concentrate can applied in a hand held pump sprayer at 2.4-4 fl oz per gallon of water. You will use the finished solution within 24 hrs of mxing. Similarly, it is asked, what is the ratio of Roundup to water? Roundup Pro To treat them, mix 6.5 ounces (13 tablespoons) to 1 gallon of water. For annual weeds in the seedling stage, add 2/3 ounce (1 1/3 tablespoons) of herbicide to 1 gallon of water. And for tough-to-control, or dense, annuals mix a solution of 2 ounces (4 tablespoons) herbicide to 1 gallon of water.How much Roundup do I need for 5 Litres of water? Application Rates & Timing Label Rate L/ha Equivalent Dilution Mls Roundup ProActive per litre water* 3 1:66 or 15 ml/litre water 4 1:50 or 20 ml/litre water 5 1:40 or 25 ml/litre water 6 1:33 or 30 ml/litre water