ABI Calculator (Ankle-Brachial Index)
HealthCalculate the ankle-brachial index (ABI) for each leg from brachial and ankle systolic pressures, with peripheral artery disease severity bands shown.
Right Arm Systolic BP
mmHg
Left Arm Systolic BP
mmHg
Right Dorsalis Pedis
mmHg
Right Posterior Tibial
mmHg
Left Dorsalis Pedis
mmHg
Left Posterior Tibial
mmHg
Ankle-Brachial Index
Right
0—
Left
0—
Overall Severity
—
Not a substitute for clinical diagnosis. ABI directly informs peripheral artery disease management decisions — always have results confirmed and interpreted by a qualified healthcare provider.
What is a ABI Calculator?
An ABI Calculator computes the ankle-brachial index — the ratio of systolic blood pressure at the ankle to systolic blood pressure at the arm — for each leg, a standard non-invasive screening test for peripheral artery disease (PAD). By entering brachial and ankle systolic pressures for both sides, this tool applies the exact method recommended in the 2012 AHA scientific statement on ABI measurement to classify PAD severity.
ABI works because arterial narrowing between the heart and ankle reduces downstream blood pressure relative to the arm. A ratio close to 1.0 suggests unobstructed flow, while a lower ratio points to progressively more significant arterial disease. This calculator reproduces that clinical calculation so patients and students can see exactly how a measured ABI value is derived.
How to use this ABI Calculator calculator
- Enter the Right Arm Systolic BP and Left Arm Systolic BP measurements.
- Enter the Right Dorsalis Pedis and Right Posterior Tibial ankle systolic pressures.
- Enter the Left Dorsalis Pedis and Left Posterior Tibial ankle systolic pressures.
- Review the calculated Right ABI and Left ABI values in the results panel.
- Check the Severity classification, which reflects the worse-affected leg.
- Discuss the results with a qualified healthcare provider, especially if either ABI falls outside the normal 1.00-1.40 range.
Formula & Methodology
ABI (per leg) = Higher Ankle Systolic Pressure (Dorsalis Pedis or Posterior Tibial) ÷ Higher Brachial Systolic Pressure (Right or Left Arm) This method follows the AHA scientific statement on ABI measurement (Aboyans V, et al. Circulation. 2012;126(24):2890-2909). Severity bands are: >1.40 noncompressible/calcified, 1.00-1.40 normal, 0.91-0.99 borderline, 0.41-0.90 mild-to-moderate PAD, and ≤0.40 severe PAD. Worked example: With brachial pressures of 130 (right) and 125 (left) mmHg, the higher brachial pressure is 130. If the right ankle readings are 100 (dorsalis pedis) and 95 (posterior tibial), the higher is 100, giving a right ABI of 100 ÷ 130 = 0.77, which falls in the mild-to-moderate PAD range. For a fuller definition, see our glossary entry on ABI.
Frequently Asked Questions
The ankle-brachial index is the ratio of systolic blood pressure measured at the ankle to systolic blood pressure measured at the arm (brachial artery), used to screen for peripheral artery disease (PAD). A lower-than-normal ratio indicates reduced blood flow to the legs, typically from narrowed or blocked arteries.
For each leg, the ABI is the higher of the dorsalis pedis and posterior tibial ankle systolic pressures, divided by the higher of the two brachial (arm) systolic pressures. Using the higher ankle reading and the higher of the two arm readings is the standard method recommended in the 2012 AHA scientific statement on ABI measurement.
An ABI between 1.00 and 1.40 is considered normal, indicating no significant arterial narrowing between the arm and ankle. Values above 1.40 often indicate noncompressible, calcified arteries rather than truly healthy blood flow, and require an alternative test to assess PAD.
An ABI of 0.90 or below indicates peripheral artery disease, with 0.41 to 0.90 classified as mild-to-moderate PAD and 0.40 or below as severe PAD. Lower scores correlate with a higher risk of leg pain on walking (claudication), non-healing wounds, and cardiovascular events overall.
An ABI above 1.40 usually means the ankle arteries are noncompressible due to calcification, common in people with diabetes or chronic kidney disease, rather than truly excellent blood flow. In these cases, alternative tests like toe-brachial index or arterial duplex ultrasound are used to assess for PAD instead.
A trained clinician uses a blood pressure cuff and a handheld Doppler device to measure systolic pressure at both arms and at the dorsalis pedis and posterior tibial arteries of both ankles, all while the patient is resting flat. The four ankle readings and two arm readings are then combined using the standard ABI formula for each leg.
Reliable ABI measurement requires a handheld Doppler ultrasound device and trained technique, so it isn't something most people can accurately perform at home with a standard blood pressure cuff. This calculator is intended to help you understand results already measured by a healthcare provider, not to replace that measurement.
Leg pain, cramping, or fatigue that occurs with walking and resolves with rest (claudication), non-healing foot or leg wounds, and known risk factors like smoking, diabetes, or high blood pressure are common reasons to request ABI screening. Discuss any of these symptoms with a qualified healthcare provider.
PAD detected by a low ABI is strongly associated with atherosclerosis elsewhere in the body, including the coronary and cerebral arteries, so an abnormal ABI often prompts broader cardiovascular risk assessment. Checking your [Blood Pressure Calculator](/blood-pressure-calculator/) result and cholesterol profile alongside ABI gives a fuller picture of vascular health.
Management typically starts with risk factor control — smoking cessation, blood pressure and cholesterol management, and supervised exercise therapy — with more severe cases sometimes requiring angioplasty or surgical revascularization. Treatment decisions depend on symptom severity and overall health, so an abnormal ABI should always be discussed with a vascular specialist or your primary care provider.
Yes, ABI can improve with risk factor management, supervised walking programs, and treatment of underlying atherosclerosis, or worsen if PAD progresses untreated. Serial ABI measurements are often used to monitor disease progression or response to treatment.
A meaningful difference between the two legs can indicate that PAD is more advanced on one side, which is why this calculator reports right and left ABI separately along with overall severity. Any significant asymmetry should be discussed with a qualified healthcare provider as part of a full vascular assessment.
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