The longest i've ever been high is when i smoked an ounce in one night with my cuz who also smoked the same amount. Admitidly we both passed out at the end, but when we woke up we was still completely out of it, and that was 4 hours later, all in all the stone lasted about 10-12 hours. I've never been able to smoke that much again though, and normally it only lasts me about 4 hours, then its just semi high.