First welcome to PB. This may help.

There are a couple of methods. I usually average the 2.

L X L X G / 1000
26 X 26 X 16 = 10.816

and
L X G X G / 800
26 X 16 X 16 = 8.32

Avg. = 9.568

http://www.pondboss.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=7;t=000401

http://www.pondboss.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=20;t=002464

http://www.pondboss.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=20;t=002868

See this link for methods.
http://floridafisheries.com/faqs/bass-size.html