ABI Calculator (Ankle Brachial Index)

Calculate the ankle-to-arm systolic pressure ratio used when screening lower-limb arterial circulation.

Ankle brachial index

Enter ankle and brachial systolic pressures measured in the same examination.

Ankle Systolic Pressure (mmHg)

Brachial Systolic Pressure (mmHg)

About the ankle brachial index

The ankle brachial index, or ABI, is a noninvasive comparison of systolic blood pressure at the ankle with systolic pressure in the arm. It is widely used to help identify peripheral artery disease, a condition in which narrowed arteries reduce blood flow to the legs. A clinician normally measures pressures after a period of rest with an appropriately sized cuff and a Doppler device. Each leg is assessed separately because circulation can differ from one side to the other. The basic formula is ankle systolic pressure divided by brachial systolic pressure. Clinical protocols generally use the higher dorsalis pedis or posterior tibial ankle pressure for a leg and the higher brachial pressure from either arm, unless a specific protocol states otherwise. This calculator accepts one selected ankle pressure and one selected brachial pressure. For example, 130 mmHg at the ankle divided by 120 mmHg at the arm gives an ABI of 1.08. Values from 1.00 through 1.40 are commonly considered normal. Values from 0.91 through 0.99 are often described as borderline. An ABI of 0.90 or lower is abnormal and may support a diagnosis of peripheral artery disease when obtained correctly. Lower values generally indicate greater hemodynamic impairment: 0.70 through 0.90 is often called mild, 0.40 through 0.69 moderate, and below 0.40 severe. Values above 1.40 may indicate stiff, poorly compressible arteries, which can occur with diabetes, chronic kidney disease, or advanced age. Thresholds and terminology vary among guidelines, laboratories, and clinical settings. A normal resting result does not always exclude disease, especially when symptoms occur during exercise. Clinicians may order an exercise ABI, toe-brachial index, pulse-volume recording, duplex ultrasound, or other vascular tests. Incorrect cuff size, patient position, inadequate rest, arrhythmia, and measurement technique can affect the ratio. This calculator cannot confirm or exclude vascular disease and should not guide treatment by itself. Seek urgent medical care for a suddenly cold, pale, painful, numb, or weak limb. Discuss exertional calf pain, slow-healing wounds, or an abnormal ABI with a qualified healthcare professional.

ABI calculation examples

The ankle pressure is divided by the brachial pressure in every example.

Pressure readings	ABI	Common category
Ankle 130 mmHg; brachial 120 mmHg	1.08	Normal range.
Ankle 72 mmHg; brachial 120 mmHg	0.60	Moderately abnormal.
Ankle 180 mmHg; brachial 120 mmHg	1.50	May indicate noncompressible vessels.

How to calculate ABI

Use a standardized vascular examination to obtain the appropriate ankle systolic pressure.
Select the appropriate brachial systolic pressure from the same examination.
Enter both pressures in mmHg and click Calculate ABI.
Review the ratio and category with symptoms, measurement technique, and professional guidance.

ABI FAQ

What is the ABI formula?

Divide the selected ankle systolic pressure by the selected brachial systolic pressure. Both readings must use the same pressure unit.

What ABI suggests peripheral artery disease?

A correctly measured resting ABI of 0.90 or lower is generally considered abnormal. A clinician considers symptoms and may confirm the finding with additional testing.

What does an ABI above 1.40 mean?

Very high values can reflect arteries that do not compress normally under the cuff. A toe-brachial index or another vascular test may be more informative.

Should each leg be calculated separately?

Yes, standard assessment reports an ABI for each leg because disease can be asymmetric. This calculator processes one leg at a time.

Can a normal ABI rule out circulation problems?

Not in every case, particularly when symptoms appear only with exercise or vessels are noncompressible. Clinical assessment determines whether further testing is appropriate.