Size Chart - Corsets
For a standard fit choose a corset size that is 4 inches smaller than your natural waist (the concave above the belly button and below the ribs) Most standard-fit corsets are intended to be worn with approximately a 2″ gap in the back lacing and a 2” waist reduction.
So if you're starting out round up to ensure you have space and if your a waist traing pro round down and pull!
For example if I'm a beginner and I have a 27 inch natural waist. I would round up to 28 and get a corset size of 24.