This will be hard to answer because roundup is sold in different strengths. On a dry morning mix a few ounces of round up to a gallon of water and test it by spaying it on some blades of grass. Results should be noticed after a few days.If you spent allot of money for just a little roundup then you probably have a strong solution. Some roundup is already mixed with water (diluted) and can be applied as is. I hope this helps