how to find sq. ft. of a radius

I have a person who wants me to extend his deck ina a existing radius. the new measurements extend the deck 17' one direction 18' at another and 15' at yet another and I am looking for the square ft. to be added so as not to charge to much or order to many materials.
any help would be great.
Pool Man

I have a person who wants me to extend his deck ina a existing radius. the new measurements extend the deck 17' one direction 18' at another and 15' at yet another and I am looking for the square ft. to be added so as not to charge to much or order to many materials.
any help would be great.

What you're wanting is the area of a sector of a circle. You need the degrees the arc of the sector subtends, also called the central angle. With the radius (r) and the central angle (in degrees), use the following formula:

Area = (Degrees * r^2 * PI)/360
where: r = radius, PI = 3.1415

A website you may find useful is: http://www.1728.com/circsect.htm

A simple curve (arc) has 1 radius, a compound curve (arc) has more than 1 radius. From the context of your question (17', 18' and 15'), I'm assuming you have more than 1 radius. More information is needed before we can give a better answer.