Ankle-Brachial Index Calculator

Systolic blood pressure measured at the ankle
Systolic blood pressure measured at the arm
Health

This ankle-brachial index (ABI) calculator screens for peripheral artery disease by comparing the blood pressure at your ankle with the pressure in your arm. Enter the systolic pressure measured at the ankle and at the arm, and it returns the ABI ratio along with a clinical interpretation of your lower-limb circulation.

Formula

ABI = Ankle Systolic BP ÷ Arm Systolic BP
  • The ABI is the ratio of systolic blood pressure at the ankle to systolic blood pressure at the arm: ABI = ankle systolic ÷ arm systolic.
  • An ABI of 0.90 to 1.30 is generally considered normal.
  • Below 0.90 suggests peripheral artery disease (PAD): 0.60-0.89 mild-to-moderate, under 0.60 severe.
  • Above 1.30 can indicate stiff, non-compressible arteries, common in diabetes or advanced age, and may need further testing.
  • Measure both pressures with the patient resting and supine, using the higher of the two ankle readings for the clinical ABI.

Example Calculation

Inputs
  • Ankle Systolic BP (mmHg): 120
  • Arm Systolic BP (mmHg): 120

With an ankle systolic pressure of 120 mmHg and an arm systolic pressure of 120 mmHg, ABI = 120 / 120 = 1.00, which falls in the normal range (0.90-1.30) and suggests no peripheral artery disease.

Frequently asked questions

What is the ankle-brachial index?
It is the ratio of the systolic blood pressure at the ankle to that at the arm, used to screen for peripheral artery disease in the legs.
What is a normal ABI?
An ABI between 0.90 and 1.30 is normal. Lower values suggest narrowed leg arteries, while higher values suggest stiff, non-compressible arteries.
What ABI indicates peripheral artery disease?
An ABI below 0.90 suggests PAD: 0.60-0.89 is mild-to-moderate and below 0.60 is severe disease.
Why can a high ABI be a problem?
An ABI above 1.30 often means the arteries are calcified and resist compression, which can mask underlying disease and warrants additional testing.
How is the measurement taken?
Systolic pressures are measured at the arm and ankle, usually with a Doppler probe and the patient lying down, and the ankle reading is divided by the arm reading.