ABI Calculator (Ankle-Brachial Index)

Written by Great Medico

Updated September 24, 2026 •2 min read

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When pressures, flows, or imaging measurements are involved, a clear equation matters. ABI Calculator (Ankle-Brachial Index) shows how the values entered combine into the reported result.

What this calculator does

The ankle-brachial index, or ABI, compares ankle systolic pressure with arm systolic pressure and is commonly used when assessing lower-extremity arterial disease. Cardiovascular measurements are highly context-dependent, and technique, symptoms, medications, and the rest of the clinical assessment can be as important as the calculated value.

How to use it

Enter or select Highest arm blood pressure, Highest pressure in right foot, and Highest pressure in left foot. Use the units offered by the calculator and keep measurements consistent when you plan to compare results over time.

How the calculation works

For each leg, the calculator divides the highest ankle/foot pressure entered by the highest brachial pressure. It reports right and left ABI and uses the lower of the two as the primary overall result.

Example

For the sample values prefilled in this calculator, the primary result is 1.067 (Lower ABI), Right ABI is 1.08, and Left ABI is 1.07. This example is there to show how the inputs flow through the implemented equation; replace the sample values with your own measurements before using the result.

How to interpret the result

Values around 1.0 to 1.4 are generally considered normal in standard ABI interpretation, 0.90 or below is abnormal, and values above about 1.40 can suggest noncompressible arteries. The leg-specific values should still be reviewed individually.

Limitations and notes

Accurate ABI requires proper cuff sizing, Doppler technique, patient rest, and appropriate arterial pressure sites. Diabetes, kidney disease, arterial calcification, wounds, or noncompressible vessels can make ABI misleading, and symptoms can warrant further vascular testing even with a seemingly normal result. For clinical use, confirm that the measurements were obtained with the technique assumed by the formula. Repeating a measurement under standardized conditions can be more informative than over-interpreting a small numerical difference.