No, it depends on the horse. The example was the OP's horse with the estimated 8" cannonbone.
If you take my mare, 1150lbs + the above 220lbs rider+45lbs tack: 9" cannonbone :2 = 78, so within the limit.
If the horse was lighter, but had the thicker bone, it would be even better.
But with my mare, even with stronger bone,I'd be a bit more careful because she is very long in the back. So, proportionally, a smaller lighter horse with short strong back can carry more than the bigger horse with long back. Has to do with center of gravity also.
Eta: just noticed, different thread regarding the OP....oops...but nevertheless, the math is right.
Last edited by deserthorsewoman; 11-16-2012 at 08:51 PM.