I've been wondering this for a while, and thinking about how the size categories work. There doesn't seem to be any official guideline to what height is qualified for each size. Mainly for the big and macro sizes.
For example, I have a character who is usually 12 feet tall, and I label him as big mechanic-wise. While I have seen someone at 11 feet or some labeled as macro. Just as I've seen people at 8 feet tall be normal and big. Is there any official guideline players should follow with this? Currently I just play it as each category is 2x the size of the one before it, and 1/2x the size of the one that is above it.