ABI Calculator (Ankle-Brachial Index)

Enter your arm and ankle systolic blood pressures to get the ankle-brachial index for each leg and screen for peripheral artery disease (PAD).

Quick Facts

Formula
ABI = higher ankle systolic / higher arm systolic pressure
Normal 1.00-1.40; 0.91-0.99 borderline; 0.90 or below suggests PAD; above 1.40 suggests noncompressible arteries.

Your Results

Calculated
Right leg ABI
-
Right ankle / higher arm pressure
Left leg ABI
-
Left ankle / higher arm pressure
Arm pressure used
-
Higher brachial systolic (denominator)
Diagnostic ABI
-
Lower of the two legs

Ready

Enter arm and ankle systolic pressures, then press Calculate.

About the ABI Calculator (Ankle-Brachial Index)

The ankle-brachial index (ABI) compares the blood pressure at your ankle to the blood pressure in your arm. When leg arteries are narrowed by peripheral artery disease (PAD), the ankle pressure drops below the arm pressure and the ratio falls below 1. This tool computes an ABI for each leg from four systolic pressures you enter and classifies the lower of the two against the standard reference bands.

The formula

For each leg, the ABI is the higher ankle systolic pressure in that leg divided by the higher of your two arm (brachial) systolic pressures:

  • Right ABI = higher right ankle pressure (dorsalis pedis or posterior tibial) / higher arm pressure.
  • Left ABI = higher left ankle pressure (dorsalis pedis or posterior tibial) / higher arm pressure.
  • Denominator = the larger of the right and left brachial systolic pressures, used for both legs.

The lower of the two leg values is the diagnostic ABI used for screening, because PAD often affects one leg more than the other.

How to measure the inputs

  • Rest lying flat for 5-10 minutes before measuring so pressures settle to a stable baseline.
  • Take systolic pressure in both arms; enter each. The higher arm reading becomes the denominator.
  • At each ankle, measure both the dorsalis pedis and posterior tibial arteries with a Doppler probe and enter the higher of the two.

Interpreting your result

An ABI of 1.00 to 1.40 is normal, 0.91 to 0.99 is borderline, and 0.90 or below suggests PAD (0.41-0.90 mild-to-moderate, 0.40 or below severe). A value above 1.40 points to noncompressible, calcified arteries, where the ankle reading is unreliable and a toe-brachial index may be used instead. A result outside the normal range is a prompt for further investigation, not a diagnosis.

When to consult a professional

This calculator is an educational screening estimate and does not replace a clinical assessment. Discuss any borderline, low, or above-1.40 result, or any leg pain, cramping, or non-healing wounds, with a licensed healthcare provider who can confirm the finding and account for your full medical history.

Frequently Asked Questions

How is the ankle-brachial index calculated?
For each leg, divide the higher systolic pressure at the ankle (dorsalis pedis or posterior tibial) by the higher of the two arm (brachial) systolic pressures. This gives a right ABI and a left ABI. The lower of the two is used to screen that person for peripheral artery disease.
What is a normal ABI result?
An ABI of 1.00 to 1.40 is considered normal. A value of 0.91 to 0.99 is borderline, 0.90 or below suggests peripheral artery disease (PAD), and a value above 1.40 suggests noncompressible, calcified arteries that can mask disease.
What does a low ABI mean?
An ABI of 0.90 or below means the ankle pressure is lower than the arm pressure, a sign of narrowed leg arteries. Values of 0.41 to 0.90 indicate mild-to-moderate PAD and 0.40 or below indicate severe PAD. This is a screening estimate, not a diagnosis, so confirm any abnormal result with a clinician.

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