See also Surviving Training: Beginner Wing, Weight & Speed, Flying Large Wings, Flying Small Wings, Risk of Small Wings
Wing loading is a key metric for many reasons. It is how much weight is carried per square meter of wing. By convention, it’s the all-up flying weight (pilot, motor, fuel, wing) divided by the wing’s flat area (as it is laid out on the ground).
Sales literature may not always include whether it’s flat or projected so double check. Add up your weights, including fuel and wing then divide that number into the wing area.
For example, a Spice 22 has a flat area near 22 m². My 145 pound self with a 70 pound paramotor and 10 pounds of gas under a 12 pound wing gives an all up flying weight of 237 lbs. Wing loading is then 237 / 22 or 10.8 lbs. per m².
This important value should be considered buying a different wing. See Choosing A Paraglider to see how.