Omaha, Nebraska is 2 times larger than Sioux Falls, South Dakota.
Area: 342 km2 calculated
Omaha is the largest city in the state of Nebraska, United States, and is the county seat of Douglas County. It is located in the Midwestern United States on the Missouri River, about 10 miles north of the mouth of the Platte River. Wikipedia
Area: 170 km2 calculated
Sioux Falls is the largest city in the U.S. state of South Dakota. It is the county seat of Minnehaha County, and also extends into Lincoln County to the south. Wikipedia