Enter the ankle systolic blood pressure (SBP) and arm/brachial systolic blood pressure (SBP) into the calculator to determine the Ankle-Brachial Index (ABI). If you already know two values, the calculator can compute the third for math-checking/educational purposes.

ABI Calculator

Enter any 2 values to calculate the third (SBP is measured; ABI is calculated from SBP).

Measurement note: ABI is calculated using systolic pressures. This calculator uses a simplified ABI = ankle SBP ÷ arm/brachial SBP; in clinical practice, ABI is commonly measured per leg using a blood pressure cuff and Doppler, often using the higher ankle artery SBP (posterior tibial or dorsalis pedis) and the higher arm SBP (protocols vary).

  • Rest quietly for about 5–10 minutes before measuring.
  • Measure systolic pressures (SBP). If you are using kPa, confirm your device reports kPa (not mmHg).
  • If measuring clinically, ABI is often calculated separately for each leg using the higher ankle artery SBP and the higher brachial SBP (method may differ by clinic/guideline).

ABI Interpretation (informational)

  • < 0.90: often associated with peripheral artery disease (PAD)
  • 0.91–0.99: sometimes considered “borderline”
  • 1.00–1.30: often considered “normal”
  • > 1.30: may suggest noncompressible/calcified arteries (interpretation may require different testing)

Medical disclaimer: For informational purposes only and not a diagnosis. If you have leg pain with walking, non-healing wounds, cool/numb feet, or sudden leg pain/weakness, seek medical care. For official interpretation and testing guidance, review consumer resources from organizations such as Mayo Clinic, MedlinePlus/NIH, or major heart/vascular societies and talk with a clinician.

ABI Formula

The following formula is used to calculate the ABI value using systolic pressures.

ABI = BPankle / BParm

Variables:

  • ABI is the Ankle-Brachial Index
  • BPankle is the ankle systolic blood pressure (SBP)
  • BParm is the arm/brachial systolic blood pressure (SBP)

To calculate the Ankle-Brachial Index, divide the ankle systolic blood pressure (SBP) by the arm/brachial systolic blood pressure (SBP). The result is the ABI value, which can help assess the likelihood of peripheral artery disease (PAD) when measured and interpreted using appropriate clinical protocols.

How to Calculate ABI?

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

  1. First, determine the ankle systolic blood pressure (BPankle).
  2. Next, determine the arm/brachial systolic blood pressure (BParm).
  3. Next, gather the formula from above: ABI = BPankle / BParm.
  4. Finally, calculate the Ankle-Brachial Index (ABI).
  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 blood pressure (BPankle) = 120 mmHg

Arm/brachial systolic blood pressure (BParm) = 140 mmHg