Ankle-Brachial Index Calculator

The ankle-brachial index compares the systolic blood pressure at your ankle to the systolic pressure in your arm. For each leg you divide the higher ankle pressure (dorsalis pedis or posterior tibial) by the higher of your two arm pressures. A lower ratio points to narrowed leg arteries, which is why the ABI is a standard non-invasive screen for peripheral artery disease.

For each leg, ABI = higher ankle systolic pressure / higher arm systolic pressure. You measure systolic pressure at both arms and at two spots on each ankle (the dorsalis pedis and posterior tibial arteries) with a Doppler probe. The denominator is the higher of the two arm readings, while each leg uses its own higher ankle reading. The reported ABI is usually the lower of the two legs.

Common resting cutoffs are: above 1.40 noncompressible (stiff, calcified arteries), 1.00 to 1.40 normal, 0.91 to 0.99 borderline, 0.41 to 0.90 mild to moderate peripheral artery disease, and 0.40 or below severe disease. A value of 0.90 or less at rest is generally considered abnormal and warrants follow-up.

Using the higher arm pressure as the denominator follows the American Heart Association method and reduces error when one arm has a subclavian stenosis. Taking the higher of the dorsalis pedis and posterior tibial pressures captures the best-perfused vessel in that foot. This convention gives the most reproducible resting ABI.

Yes. In people with diabetes or advanced kidney disease, ankle arteries can become calcified and resist compression, which pushes the ABI above 1.40 and can mask real disease. When that happens, clinicians often use a toe-brachial index or imaging instead. An exercise (post-treadmill) ABI can also unmask disease that looks normal at rest.

No. This calculator is for education only and is not a diagnosis or a substitute for professional medical advice. Cuff size, probe technique, and timing all affect the reading, and a single resting ABI cannot rule disease in or out. Share any abnormal or borderline result with a clinician who can confirm it and decide on next steps.