"Depends on which strength of Round-up You have.
Roundup Concentrate
Dilution rates are the same for both the old (18% glyphosate) and the current (25% glyphosate) formulations.
For Best Results: Use 6 fluid ounces (12 tablespoons) of Roundup Concentrate per gallon of water.
For Easy to Kill Weeds (such as weed seedlings): Use 3 fluid ounces (6 tablespoons) of Roundup Concentrate per gallon of water.
Roundup Super Concentrate
Dilution rates are the same for both the old formulation (41% glyphosate) and the current formulation (50% glyphosate).
For Best Results: Use 2.5 fluid ounces (5 tablespoons) of Roundup Concentrate per gallon of water.
For Easy to Kill Weeds (such as weed seedlings): Use 1.5 fluid ounces (3 tablespoons) of Roundup Concentrate per gallon of water.
Roundup Brush Killer
Amount to Use: Use 6 fluid ounces (12 tablespoons) of Roundup Brush Killer Concentrate per gallon of water"
Hope this helps