The durable D-ring contoured cuff (CD-CS9) fits arms 7" to 9" in circumference. Before you purchase a home blood pressure monitor, it's important to determine the best cuff size for you. To determine your arm 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 the Advanced Accuracy Blood Pressure Monitor Series and Blood Pressure Monitor models: BP710N, BP742N, BP5100, BP7100.