The easiest way of measuring hems is to turn the skirt inside out & put it on the ironing board with the waist at the pointy end . Measure from under the waistband to the finished length you want + hem & mark with a pin, or chalk .
It’s a great way of levelling up & you can cut off what is left over
The ironing board supports the weight of the fabric, & allows for accurate measurement
Decide on how big a hem you want - say for arguments sake that it is an inch, then, having clean-finished the raw edge, you can go around the hem pressing up 1" with your iron, pin it, & sew it at your leisure, either by machine, or hand
I do hope that you have an ironing board, & iron somewhere, as you can’t sew without them