Lay your best fitting jeans down on a flat surface and then measure the following:
The measurement from the top of the waistband down to the bottom of the crotch seam.
If you are unsure of where your new jean will sit on your waist measure from the crotch upwards to the top of the waistband. This measurement will give you the correct measurement of where the jeans you are looking at will sit on your body. Remember, you may want to make a note of this measurement.
The inseam is the measurement of the inside leg to take this measure from the crotch down the leg to the ankle.
Take the measurement from the smallest part of your waist which is your natural waistline, above your navel and below your ribcage. Measure straight across. Note that your actual waist measurement will not equal jean waist size. For example, a person with a 26-inch waist typically wears jeans with a 28-inch waist.
Stand with your feet together take the tape measure around your bottom and measure the fullest part of your hips at the top of your legs, approx 9 inches lower than your waistline.
The leg opening
This is the measurement that will tell you how wide the opening of the leg of your new jeans will be. Measure the circumference of the bottom of the hem.