In order to properly measure your hips, you will need to use a cloth measuring tape approximately 60 inches long. You want a tape that is used by a seamstress or tailor not a carpenter's retractable tape measure or a wooden ruler.
To get the most accurate hip measurement you will need to wear very tight-fitting clothing such as a bathing suit or spandex sport's attire, your underwear or nothing at all.
If you have access to a full-length mirror, stand square in front of it with tape measure in hand. Determine the widest part of your buttocks. With the starting end of the tape measure in your left hand pull the tape with your right hand across the widest part of your backside. Hold the start of the tape flat against your abdomen so that it is perpendicular to the tape going across the back while holding the line parallel to the ground. Be sure your tape measure is not twisted or slacking. Pull the remainder of the tape found in your right hand taut, but not tight, to meet the starting point of the tape measure held by your left hand. The tape measure should lay flat against the skin and should not pinch the skin or make an indentation. Look in the mirror to read the measurement as opposed to looking or bending down so that the body remains in the best possible position to get the most accurate reading. Take two measurements, and determine the average.
If you do not have access to a full-length mirror, ask a friend to help. It's best if you can stand on a chair or stool. Have your friend take a few steps back to look at your overall shape then find the widest part of your buttocks. Your friend should bring the tape measure around that broadest point from the back to front securing the start of the tape at the front of your abdomen and wrapping the remaining tape around the buttock keeping the tape level and bringing it to that front starting point. Be certain the tape is not twisted or slacking. Your friend will pull the tape taut but not too tight. Line the points up to find the measurement.