U-shaped stairs

The two flights run parallel in opposite directions after the stairway turns roughly 180 degrees at the landing. That puts two flights into roughly the length of one, which is why it suits a tight footprint.

Yes. Two flights share a single riser height because the calculator divides the total rise between them, which makes every step in either flight identical.

At the landing a U-shaped stairway turns roughly 180 degrees, so its two flights run parallel in opposite directions. An L-shaped stairway makes a single corner turn, which is a 90 degree change in direction.

U-shaped stairs are also called switchback stairs or half-turn stairs. The two flights run parallel to each other and turn 180 degrees at the landing.

You need roughly twice the stair width across, because the two flights sit side by side. In depth, you need the longer flight's run plus a landing, and the landing's depth equals the stair width. When you enter the rise, riser cap and tread, the calculator reports both runs.

A U-shaped staircase with a 9 foot rise, 36 inch wide stairs and 10 inch treads needs about a 6 by 8 foot footprint: 6 feet across for the two flights side by side, and 8 feet deep including the landing. This example uses 14 risers at about 7.71 inches each, split into two flights of 7. Each flight runs 60 inches, and the 36 inch deep landing brings the total depth to 8 feet. The exact footprint changes with rise, width and tread depth.