Well its easy to measure but you I don't believe you can use those measurements to any good. My point is that we are talking about millimeters here. I bet new chains of different brands or even models will have different measurements when we are down to millimeters. The difference between good and worn out chain is so small that even factors such as temperature can make a good chain measure as "worn out" and vice verca. Best indication imo is when you can't ride anymore. Chainrings are heavy duty so they should be fine by then, and you should just have to replace chain and casette. This should be every 5 years or so.