Enter the measured ankle systolic pressure (mmHg) and the brachial systolic pressure (mmHg) into the calculator to compute the Ankle-Brachial Index (ABI) (also called ABPI). If you measured multiple sites, typically use the higher ankle artery pressure for the leg being assessed and the higher brachial pressure (unless your clinician instructs otherwise).

Ankle-Brachial Index (ABI) Calculator

Enter the measured ankle and brachial systolic pressures to calculate ABI (unitless ratio).

Tip: If you have multiple readings, clinicians often use the higher ankle artery pressure for the leg and the higher brachial pressure (unless advised otherwise).

Medical disclaimer: This calculator is for educational purposes only and does not provide medical advice or a diagnosis. ABI measurement technique and interpretation should be performed or confirmed by a qualified healthcare professional (especially if you have diabetes, kidney disease, or suspected calcified/noncompressible arteries). If you have severe symptoms such as rest pain, a suddenly cold/pale/blue foot, sudden worsening leg pain, or non-healing wounds, seek urgent medical care or call your local emergency number.

Ankle-Brachial Index (ABI) Formula

ABI = ASP / BSP

Variables:

  • ABI is the Ankle-Brachial Index (unitless ratio; also called ABPI)
  • ASP is the ankle systolic pressure (mmHg)
  • BSP is the brachial systolic pressure (mmHg)

To calculate the Ankle-Brachial Index, divide the ankle systolic pressure by the brachial systolic pressure.

How to Calculate Ankle-Brachial Index?

The following steps outline how to calculate the Ankle-Brachial Index.

  1. First, determine the ankle systolic pressure (mmHg).
  2. Next, determine the brachial systolic pressure (mmHg).
  3. Next, gather the formula from above: ABI = ASP / BSP.
  4. Finally, calculate the Ankle-Brachial Index.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

ankle systolic pressure (mmHg) = 120

brachial systolic pressure (mmHg) = 130

ABI = 120 / 130 = 0.923

Frequently Asked Questions

What is the Ankle Brachial Index (ABI) used for?
The Ankle Brachial Index (ABI) (also called ABPI) is a simple, non-invasive test used to screen for peripheral arterial disease (PAD), a condition in which the arteries in the legs are narrowed or blocked. It can also help assess the severity of reduced blood flow when interpreted in clinical context.

How is the Ankle Brachial Index (ABI) test performed?
The ABI test is performed by measuring blood pressure in both arms (brachial pressure) and at the ankles (ankle systolic pressure) using a blood pressure cuff and a Doppler device. Clinicians commonly use the highest ankle pressure for the leg being assessed divided by the highest brachial pressure (unless a clinician uses a different convention based on your situation).

What does an ABI value indicate?
In general clinical practice, ABI ranges are sometimes described as: 1.0 to 1.4 often considered normal, 0.9 or less suggestive of PAD, and above 1.4 possibly indicating noncompressible (calcified) arteries that need further evaluation. Interpretation depends on measurement technique, symptoms, and medical history.

Can the Ankle Brachial Index (ABI) test be done at home?
While the ABI test is typically performed by healthcare professionals in a clinical setting, there are portable devices available for home use. It’s important to have the results interpreted by a healthcare provider to ensure accuracy and appropriate follow-up.

Sources and Further Reading

  • Look for patient education pages on “Ankle-Brachial Index (ABI)” from major hospital/health system websites.
  • Review peripheral artery disease (PAD) guideline summaries from major cardiology/vascular societies (e.g., ACC/AHA) for ABI technique and interpretation.
  • Check NIH MedlinePlus (or similar national health resources) for an overview of PAD and ABI testing.