The coverage area would depend on the concentration with which you mix the Roundup. Please refer to the manufacturers label for your specific situation and the table on page 3 to determine the percent solution of water to Roundup ratios.

From the Label:
Use 26 fluid ounces per acre if weeds are less than 6 inches in height or runner length
and 1.2 to 3.2 quarts per acre if weeds are over 6 inches in height or runner length or
when weeds are growing under stressed conditions. Use the higher rate for tough-to-
control species regardless of the weed size at application. Treat tough-to-control weeds
early when they are relatively small. This product may be tank mixed provided that the
specific tank mix product is registered for use on the target site. Refer to these product
labels for approved sites and application rates. Read and carefully observe the cautionary
statements and all other information appearing on the labels of all herbicides used. Use
according to the most restrictive precautionary statements for each product in the mixture.
For spray-to-wet applications, apply a 0.4 percent solution of this product to weeds less
than 6 inches in height or runner length. Apply prior to seedhead formation in grass or bud
formation in broadleaf weeds. For annual weeds over 6 inches tall, or for smaller weeds
growing under stressed conditions, use a 0.8 to 1.6 percent solution. Use the higher rate
for tough-to-control species or for weeds over 24 inches tall.