Lay your fabric out flat on the floor and measure your height + hem allowance number from bottom to top. Measure every foot or so, marking the measurement with your chalk. In this way, you will be marking it all the way down and it will be easier to cut. Cut along the dashed lines you just made, all the way down the fabric.
Fold the long edge of the fabric in half. Cut along the crease to make two large pieces, one for the front of the skirt, and one for the back. Separate the pieces and fold each piece in half again, lengthwise, the same direction you folded it before.
Now you can measure your panels.