Ankle-Brachial Index Calculator
The ankle-brachial index (ABI) compares blood pressure at the ankle to blood pressure at the arm to screen for peripheral artery disease. For each leg you take the higher of its two ankle systolic pressures (dorsalis pedis or posterior tibial) and divide by the higher of the two arm systolic pressures. A low ratio suggests narrowed leg arteries, while a very high ratio suggests stiff, calcified vessels. This calculator computes the right and left ABI plus the lower overall value used for screening. Enter all pressures in mmHg. It is educational and not a diagnosis.
ABI formula
Higher arm = max(right arm, left arm)
Right ABI = right ankle / higher arm
Left ABI = left ankle / higher arm
Overall ABI = min(right ABI, left ABI)
All pressures in mmHg; index is unitless
In a full clinical test each ankle has two pressures (dorsalis pedis and posterior tibial) and the higher is used. This calculator takes the already-selected higher ankle pressure per leg.
ABI interpretation thresholds
- Above 1.40: non-compressible, calcified arteries.
- 1.00 to 1.40: normal.
- 0.91 to 0.99: borderline.
- 0.90 or below: peripheral artery disease.
- 0.40 or below: severe peripheral artery disease.
Ankle-brachial index: frequently asked questions
How is the ankle-brachial index calculated?
For each leg, ABI equals the higher of that leg's ankle systolic pressures (dorsalis pedis or posterior tibial) divided by the higher of the two arm (brachial) systolic pressures. The overall ABI for screening is usually the lower of the two leg values.
What ABI value is normal?
An ABI between 1.00 and 1.40 is generally normal. Values of 0.91 to 0.99 are borderline, 0.90 or below suggests peripheral artery disease, and above 1.40 suggests non-compressible, calcified arteries. These thresholds follow widely used vascular guidance.
Why use the higher arm pressure?
Using the higher of the two brachial pressures accounts for the possibility of subclavian artery stenosis on one side, which would falsely lower the arm pressure and distort the index.
What units are used?
All four pressures are systolic blood pressures in mmHg. The index itself is a unitless ratio because the two pressures share the same unit.
Is this a diagnosis?
No. ABI is a screening estimate for peripheral artery disease. A low or high value should prompt clinical evaluation. This calculator is for education and does not replace assessment by a qualified clinician.
Official sources
- National Heart, Lung, and Blood Institute: Peripheral artery disease information.
- American Heart Association (professional): ABI measurement guidance.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.