Body measurement to size conversion tables are essential for online clothes shopping. A lot of places seem to include a standard size-to-size conversion chart for different (unreliable) sizing standards around the world, which is not quite good enough. To be sure you're going to fit something, you need to know how it relates to actual body measurements.
Mokalus of Borg
PS - The same goes for shoes and hats.
PPS - Anything, really, where measurement is critical and non-standard.