Measure with a paper measuring tape.
Be sure to stand up straight when measuring.
Make sure the tape is snug. Not too tight and not too loose.
If you are wearing waist beads to lose weight, measure around your stomach. Your beads will fall as you lose weight.
If you will be wearing the beads over your clothes, then take you measurement with your clothes on.
Record your measurement and proceed to order your body enhancements.