acalculator

What is the ABI?

Enter the systolic pressures in both arms and at both ankle arteries of each leg to get the ankle-brachial index (ABI) of each leg and its grade. For information only. This is not medical advice or a diagnosis. Do not use it to make treatment decisions without a clinician. No licensed clinician has reviewed this page.

Your numbers

ABI (lower leg)
0.8

The ABI is 0.92 on the right (Borderline) and 0.8 on the left (Abnormal).

Abnormal (0.90 or less)

  1. Abnormal (0.90 or less)
  2. Borderline (0.91 to 0.99)
  3. Normal (1.00 to 1.40)
  4. Noncompressible (over 1.40)
Right ABI
0.92
Right leg
Borderline
Left ABI
0.8
Left leg
Abnormal

ABI (lower leg): 0.8. The ABI is 0.92 on the right (Borderline) and 0.8 on the left (Abnormal).

ABI of the lower leg

This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use

How to calculate

Works out the ankle-brachial index (ABI) for each leg from the arm and ankle systolic pressures, as the 2016 AHA/ACC guideline on peripheral artery disease defines it, and grades each result.

Example with the default inputs (Right arm (brachial) 130, Left arm (brachial) 128, Right ankle, posterior tibial 120, Right ankle, dorsalis pedis 118, Left ankle, posterior tibial 100, Left ankle, dorsalis pedis 104): The ABI is 0.92 on the right (Borderline) and 0.8 on the left (Abnormal).

Method: ABI (each leg) = higher of the dorsalis pedis and posterior tibial systolic pressures ÷ higher of the right and left arm systolic pressures. Rounded to 2 decimals, then graded: 0.90 or less abnormal, 0.91 to 0.99 borderline, 1.00 to 1.40 normal, over 1.40 noncompressible.

  • Systolic pressures measured with a cuff and a Doppler probe while lying down.
  • Each ABI is rounded once to 2 decimals (halves up) from the exact ratio of the typed pressures, then graded.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Right arm (brachial) 130, Left arm (brachial) 128, Right ankle, posterior tibial 120, Right ankle, dorsalis pedis 118, Left ankle, posterior tibial 100, Left ankle, dorsalis pedis 104 gives ABI (lower leg) 0.8, Right ABI 0.92, Right leg Borderline, Left ABI 0.8, Left leg Abnormal.Source: 2016 AHA/ACC guideline rule: right 120 ÷ 130 = 0.923 → 0.92 borderline
  2. Right arm (brachial) 120, Left arm (brachial) 124, Right ankle, posterior tibial 130, Right ankle, dorsalis pedis 126, Left ankle, posterior tibial 128, Left ankle, dorsalis pedis 132 gives ABI (lower leg) 1.05, Right ABI 1.05, Right leg Normal, Left ABI 1.06, Left leg Normal.
  3. Right arm (brachial) 140, Left arm (brachial) 140, Right ankle, posterior tibial 126, Right ankle, dorsalis pedis 120, Left ankle, posterior tibial 200, Left ankle, dorsalis pedis 210 gives Right ABI 0.9, Right leg Abnormal, Left ABI 1.5, Left leg Noncompressible.
  4. Right arm (brachial) 100, Left arm (brachial) 98, Right ankle, posterior tibial 99, Right ankle, dorsalis pedis 90, Left ankle, posterior tibial 140, Left ankle, dorsalis pedis 135 gives Right ABI 0.99, Right leg Borderline, Left ABI 1.4, Left leg Normal.
  5. Right arm (brachial) 200, Left arm (brachial) 180, Right ankle, posterior tibial 181, Right ankle, dorsalis pedis 170, Left ankle, posterior tibial 199, Left ankle, dorsalis pedis 150 gives Right ABI 0.91, Right leg Borderline, Left ABI 1, Left leg Normal.

Medical disclaimer

This calculator is for information and education only. It is not medical advice, and its result is not a diagnosis. Do not use it to start, stop, or change a treatment without a clinician who knows your health history. No licensed clinician has reviewed this page. This site's editors checked the formulas and worked examples against published sources. If you think you have a medical emergency, call your local emergency number.

When this does not apply. The guideline uses the resting ABI for adults with symptoms or risk of peripheral artery disease. Stiff, noncompressible arteries (ABI over 1.40) hide narrowing. A normal resting ABI does not rule out disease that shows only with exercise.

How the index is worked out

  1. Arm pressure = the higher of the right and left brachial systolic pressures.
  2. Right ABI = the higher of the right dorsalis pedis and right posterior tibial pressures ÷ the arm pressure.
  3. Left ABI = the higher of the left dorsalis pedis and left posterior tibial pressures ÷ the arm pressure.
  4. Each ABI is rounded once to 2 decimals, halves up, from the exact ratio of the typed pressures.
  5. Grade (2016 AHA/ACC guideline): 0.90 or less abnormal; 0.91 to 0.99 borderline; 1.00 to 1.40 normal; over 1.40 noncompressible.

The headline is the lower of the two legs. Pressures are systolic, in mmHg, from 20 to 300.

Worked examples by hand

Page default. Arms 130 and 128: arm 130. Right ankle 120 and 118: 120 ÷ 130 = 0.923, 0.92, borderline. Left ankle 100 and 104: 104 ÷ 130 = 0.80, abnormal. Headline 0.80.

Both normal. Arms 120 and 124: arm 124. Right 130 ÷ 124 = 1.048, 1.05. Left 132 ÷ 124 = 1.064516…, 1.06. Both normal.

Edge and stiff arteries. Arms 140 and 140. Right 126 ÷ 140 = 0.90, abnormal (0.90 or less). Left 210 ÷ 140 = 1.50, noncompressible.

Band edges. Arms 100 and 98: arm 100. Right 99 ÷ 100 = 0.99, borderline. Left 140 ÷ 100 = 1.40, normal.

Exact halves. Arms 200 and 180: arm 200. Right 181 ÷ 200 = 0.905, rounds up to 0.91, borderline. Left 199 ÷ 200 = 0.995, rounds up to 1.00, normal.

Other questions people ask

How is the ABI calculated?

For each leg, take the higher of the two ankle pressures (dorsalis pedis and posterior tibial) and divide it by the higher of the two arm pressures. The 2016 AHA/ACC guideline on peripheral artery disease defines it this way.

What is a normal ABI?

The guideline grades an ABI of 1.00 to 1.40 as normal, 0.91 to 0.99 as borderline, 0.90 or less as abnormal, and over 1.40 as noncompressible.

What does an ABI of 0.90 or less mean?

The guideline calls it abnormal and uses it to support a diagnosis of peripheral artery disease (narrowed leg arteries), together with symptoms and an exam. The number alone is not a diagnosis.

What does an ABI over 1.40 mean?

The ankle arteries are too stiff to squeeze shut with the cuff (noncompressible), which is common with diabetes or kidney disease. The ABI then cannot show narrowing, and the guideline suggests a toe-brachial index instead.

Why use the higher arm pressure?

A narrowing in one arm artery can make that arm read low. The higher arm pressure is the better estimate of the pressure in the aorta.

Why does the page round before it grades?

The guideline bands are written to 2 decimals (0.90, 0.91, 0.99, 1.00, 1.40). The page rounds each ABI once to 2 decimals, halves up, and grades that value, so 0.905 is 0.91, borderline.