Boot Shaft: This is the part of the boot that covers the leg.
Shaft Height: This measurement is taken on the inside seam of the boot, and is measured from where the shaft meets to sole of the boot, to the top of the shaft. To determine where the top of a boot will hit on your leg, measure the height of the shaft against the inside of your leg, starting at your instep.
Circumference:This is the measurement around widest part of the shaft of the boot.
To see if tall boots will fit your calves, measure around the widest part of your calf, and compare your measurement to the shaft circumference.