About the Ankle-Brachial Index Calculator
The ankle-brachial index (ABI) compares the systolic blood pressure at the ankle with the pressure in the arm. In healthy legs the ankle pressure is equal to or slightly higher than the arm pressure, so the ratio is about 1.0–1.4. Narrowed leg arteries from peripheral artery disease (PAD) lower the ankle pressure and the ABI.
This calculator follows the method in the 2024 ACC/AHA multisociety guideline on lower extremity PAD (which keeps the 2016 categories): measure systolic pressures with a Doppler probe in both arms (brachial arteries) and at both ankles (dorsalis pedis and posterior tibial arteries) with the patient supine. Each leg’s ABI is the higher of its two ankle pressures divided by the higher of the two arm pressures, conventionally reported to two decimal places.
Results are reported using the guideline categories: abnormal (≤ 0.90), borderline (0.91–0.99), normal (1.00–1.40) and noncompressible (> 1.40), which is common with diabetes or chronic kidney disease; the guideline then recommends a toe-brachial index (abnormal at 0.70 or less). The ABI supports, but does not replace, assessment by a clinician.
With the default inputs, the abi (lower of the two legs) is 0.77. Change any value above to recalculate instantly.
How to use the ankle-brachial index calculator
- 1Lay the patient supine and let them rest for 5–10 minutes.
- 2Measure systolic pressure in both arms with a Doppler probe.
- 3Measure dorsalis pedis and posterior tibial systolic pressures at each ankle.
- 4Enter all six values (use 0 for any pulse you could not obtain).
- 5Read each leg’s ABI and category; the lower leg value is the patient’s ABI.
Formula and method
Systolic pressures are measured with a hand-held Doppler with the patient supine, usually after 5–10 minutes of rest. For each leg the higher of the two ankle pressures is divided by the higher of the two arm pressures, and the result is rounded to two decimal places by convention. The patient’s overall ABI is usually taken as the lower of the two legs.
The 2024 ACC/AHA guideline (like the 2016 version) reports resting ABI as abnormal (≤ 0.90), borderline (0.91–0.99), normal (1.00–1.40) or noncompressible (> 1.40). An ABI of 0.90 or less establishes the diagnosis of PAD in a patient with history or examination findings suggestive of it; values above 1.40 mean the ankle arteries are too stiff to compress, which hides disease rather than excluding it.
- ABI
- Ankle-brachial index
- DP, PT
- Dorsalis pedis and posterior tibial artery systolic pressures (mmHg)
- Brachial
- Arm systolic pressure (mmHg); the higher of both arms is used
Worked examples
Left-leg claudication
The higher arm pressure is 130. Right ABI = 125 ÷ 130 = 0.96 (borderline); left ABI = 100 ÷ 130 = 0.77, which is abnormal and diagnostic of PAD in the left leg.
Normal result
Using the higher arm pressure of 122: right 138 ÷ 122 = 1.13 and left 136 ÷ 122 = 1.11. Both lie in the normal 1.00–1.40 range.
Diabetes with stiff arteries
Right ABI = 220 ÷ 140 = 1.57, above 1.40, so the right ankle arteries are noncompressible and a toe pressure is needed. Left ABI = 150 ÷ 140 = 1.07 is normal.
Frequently asked questions
What is a normal ankle-brachial index?+
A resting ABI of 1.00 to 1.40 is normal. Values of 0.91–0.99 are borderline, 0.90 or below is abnormal and diagnostic of peripheral artery disease, and above 1.40 indicates noncompressible (calcified) arteries.
How is the ABI calculated?+
For each leg, divide the higher of the dorsalis pedis and posterior tibial systolic pressures by the higher of the two brachial (arm) systolic pressures. Report each leg separately to two decimal places.
What does an ABI above 1.4 mean?+
It means the ankle arteries are stiff and cannot be compressed by the cuff, often because of calcification in diabetes or chronic kidney disease. PAD may still be present, so a toe-brachial index or imaging is used instead.
What ABI indicates severe PAD?+
Grading within the abnormal range varies, but values below about 0.40 are commonly described as severe disease and are associated with rest pain and critical limb ischaemia. Interpretation always depends on symptoms and other tests.
Can I use an automated blood pressure cuff for ABI?+
The guideline method uses a blood pressure cuff with a hand-held Doppler, which is the reference standard. Some oscillometric devices are validated for ABI, but they are less accurate at low ankle pressures, where PAD is most likely.
For healthcare professionals and education only. This calculator implements a published formula or score but is not a diagnosis and does not replace clinical judgment. Verify inputs and results against the original source before using them in patient care.