The Ollie chair is BIFMA-certified, which means it has been tested to meet a set of furniture-specific safety and performance standards. As part of that testing, the chair needs to withstand a drop of a 300 lb (136 kg) sandbag from 6 inches (152 mm) above the seat; that 6 inch (152 mm) drop is a very close simulation of a real person actually sitting down. So in terms of applied direct weight, we can confirm the chair is (and feels) sturdy up to 300 lbs (136 kg).
We also completed some additional "real subject" testing (as opposed to "in-facility" testing) where we put in excess of 370 lbs on the chair without issue -- note that we're not actually certified up to that weight and would advise against using the chair at or above the parameters certified in the BIFMA testing, but it can be helpful to understand how the chair base responds when it is overstressed. See a video of the results on our main campaign page or follow this link: http://bit.ly/OllieWeightTest.