A quick Google search on "oar length calculation" brought up this link:

http://www.shawandtenney.com/wooden-rowing-oars.htm

Look towards the lower part of the page.

Tom Dacon

"Dan Listermann" wrote in message
...
We bought a 14' x 5' johnboat. It did not come with oars and I want to
buy some. How long should they be? I am about 5' 6" tall if that is
important.