Found a good Sail wind load calculator on the internet.
You type in your sail size & then the wind speed and it tells you the load on your sail. Only problem is you have to enter your sail size in square feet.


www.sailingusa.info/cal_wind_load.htm

www.embassyworld.com/data/Square_Meters_Square_Feet.html
to convert square metres to square feet.

Don't forget it is for yachts..those slow things you sail around on your windsurfer.

Square reaching at 28knots in 21knots of wind gives an appartant wind of 35knots.

Multiplying your sail size by 10 will get you close to the square foot area.