Use a flexible measuring tape or a strip of paper
Bring your thumb and little finger together as if putting on a bangle
Measure around the widest part of your hand, usually across the knuckles
If using paper, mark the point where it overlaps
Measure the marked length with a ruler
Compare the measurement to a bangle size chart
Choose the bangle size that matches or is slightly larger than your hand measurement
If between sizes, select the larger size