The soft, contoured Omron small D-ring cuff wide range cuff fits arms 7 in. To 9 in. In circumference. Before you purchase a home blood pressure Monitor, it's important to determine the best cuff Size for you. To determine your appropriate cuff Size, Use a cloth measuring tape and measure the circumference of your left upper arm, midway between your elbow and shoulder. Ensuring that the blood pressure cuff is neither too tight nor too loose will help ensure the most Accurate readings, providing you a more accurate picture of your heart's health. This cuff is only compatible with Omron blood pressure Monitor models: BP5350, BP5450, and BP7900.