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Ankle-brachial index (ABI) calculator for peripheral artery disease

Enter the systolic pressures measured at both arms and both ankles to calculate the ABI for each leg and interpret it.

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Results

Lower ABI (the one used for diagnosis)

0.73

0.41–0.90: peripheral artery disease
Right leg ABI
0.92
Left leg ABI
0.73
Arm pressure used (higher of the two arms)
130 mmHg
Difference between the arms
2 mmHg

What the ankle-brachial index is

The ankle-brachial index (ABI) compares blood pressure at the ankle with blood pressure in the arm. In healthy people, pressure at the ankle is equal to or slightly higher than in the arm. When the leg arteries are narrowed by atherosclerosis, peripheral artery disease (PAD), pressure at the ankle drops. The ABI is quick, painless and the standard first test for PAD.

How it is measured

  1. The patient lies flat for about 10 minutes.
  2. A cuff and a handheld Doppler probe measure the systolic pressure in both arms (brachial arteries).
  3. At each ankle, the pressure is measured in the dorsalis pedis and posterior tibial arteries.

ABI for each leg = higher ankle pressure on that side ÷ higher of the two arm pressures

The lower of the two legs’ values is used for the diagnosis.

Worked example

Site Systolic pressure
Right arm 130 mmHg
Left arm 128 mmHg
Right ankle 120 mmHg
Left ankle 95 mmHg
  • Right ABI = 120 ÷ 130 = 0.92, borderline
  • Left ABI = 95 ÷ 130 = 0.73, consistent with PAD in the left leg

Interpretation (AHA/ACC)

ABI Meaning
Above 1.40 Non-compressible, calcified arteries; result unreliable
1.00–1.40 Normal
0.91–0.99 Borderline
0.41–0.90 Mild to moderate PAD
0.40 or less Severe PAD, risk of critical limb ischemia

An ABI of 0.90 or less is highly specific for a significant narrowing on angiography, although it can miss some cases, especially in people with calcified arteries.

Why it matters beyond the legs

PAD is a marker of atherosclerosis elsewhere. A low ABI roughly doubles the risk of heart attack, stroke and cardiovascular death, even without leg symptoms. Treatment focuses on stopping smoking, regular walking, blood pressure and cholesterol control and, often, antiplatelet therapy.

Special cases

  • In people with diabetes or chronic kidney disease, calcified arteries can give a falsely normal or high ABI; a toe-brachial index is then more reliable.
  • A difference of 15 mmHg or more between the arms suggests a narrowed subclavian artery and is itself a cardiovascular risk marker.
  • If symptoms suggest PAD but the resting ABI is normal, an exercise ABI on a treadmill can unmask it.

This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.

Frequently asked questions

How is the ankle-brachial index calculated?

For each leg, divide the higher systolic pressure measured at the ankle (dorsalis pedis or posterior tibial artery) by the higher of the two arm pressures. With an arm pressure of 130 and an ankle pressure of 95, the ABI is 0.73.

What is a normal ABI?

Between 1.00 and 1.40. Values of 0.91 to 0.99 are borderline, 0.90 or less indicates peripheral artery disease, and above 1.40 suggests stiff arteries that the cuff cannot compress.

Who should have an ABI test?

People with leg pain on walking that eases at rest, non-healing leg or foot wounds, or a high risk of artery disease, such as smokers and people with diabetes over 50 or anyone over 65. Discuss it with your doctor.

Why use the higher arm pressure?

A narrowed subclavian artery can lower the pressure in one arm. The higher arm reading is the better estimate of central blood pressure.

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Results are estimates provided for information purposes. They do not replace professional advice.

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