You can try the datasheet, or you could try some basic arithmetic.
If it is on two sprockets:
PHP Code:
Here it is:
/\--------/\
\/--------\/
\ \
\ +sprocket
+belt
as per that ascii art, basically find:
the circumference of ONE sprocket (because you have 2)
Add that to the distance between the center points of the sprockets, times 2.
subtotal those and you should be off in flames!