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Ankle-Brachial Index (ABI) Calculator for Both Legs

Calculate the ankle-brachial index for each leg from arm and ankle (DP and PT) systolic pressures, with PAD grading, arm-difference check and optional toe-brachial index.

Right arm (brachial) systolic

Left arm (brachial) systolic

Right ankle: dorsalis pedis (DP) systolic

Right ankle: posterior tibial (PT) systolic

Left ankle: dorsalis pedis (DP) systolic

Left ankle: posterior tibial (PT) systolic

Severity grading

Add toe pressures (toe-brachial index)

Right big-toe systolic

Left big-toe systolic

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How it works

ABI (each leg) = highest ankle systolic pressure in that leg (dorsalis pedis or posterior tibial) ÷ highest brachial systolic pressure (either arm), recorded to 2 decimals · TBI = big-toe systolic pressure ÷ highest brachial systolic pressure · AHA/ACC style: over 1.40 noncompressible, 1.00–1.40 normal, 0.91–0.99 borderline, 0.90 or less PAD (0.41–0.90 mild to moderate, 0.40 or less severe)

The ankle-brachial index compares the blood pressure at your ankle with the pressure in your arm. In healthy legs the ankle pressure is about the same as the arm pressure or a little higher, so the ratio is 1.00 to 1.40. Narrowed leg arteries (peripheral artery disease, PAD) lower the pressure that reaches the ankle, and a ratio of 0.90 or less is the accepted threshold for PAD. A ratio above 1.40 usually means the ankle arteries are too stiff and calcified to be compressed by the cuff, so the test is unreliable and a toe-brachial index is used instead. The standard method takes the systolic pressure in both arms and uses the higher one for both legs, then takes the dorsalis pedis (top of the foot) and posterior tibial (inner ankle) pressures in each leg and uses the higher one for that leg. The calculator does this for both legs, reports the leg that matters most, grades it on the AHA/ACC-style scale or the clinic scale used in many wound-care and vascular clinics, and flags an arm-to-arm difference of 15 mmHg or more, ankle pressures under 50 mmHg and missing readings. Turn on toe pressures to get a toe-brachial index (0.70 or more is normal). The mean arterial pressure calculator describes one arm reading; the ABI instead compares two sites to find blocked leg arteries. It interprets measurements taken by a clinician with a Doppler; it cannot diagnose PAD by itself.

Worked example

Arm pressures are 132 mmHg (right) and 128 mmHg (left), so 132 mmHg is used. The right ankle reads DP 120 and PT 126 mmHg, so the right ABI is 126 ÷ 132 = 0.955, recorded as 0.95: borderline. The left ankle reads DP 96 and PT 90 mmHg, so the left ABI is 96 ÷ 132 = 0.727, recorded as 0.73: below 0.90, so mild to moderate PAD on the AHA/ACC-style scale (moderate PAD on the clinic scale). The left leg is the one that counts, and the 4 mmHg arm difference is not significant.

Sources: Stanford Medicine 25: Measuring and understanding the ankle-brachial index · Radiopaedia: Ankle-brachial index (normal, borderline, PAD and severe cutoffs) · FPnotebook: Ankle brachial index (noncompressible vessels, ankle pressure, toe-brachial index) · Omni Calculator: ABI (90 mmHg arm, 110 mmHg ankle example)

Frequently asked questions

What is a normal ankle-brachial index?

A resting ABI of 1.00 to 1.40 is normal. 0.91 to 0.99 is borderline, 0.90 or less indicates peripheral artery disease, and above 1.40 suggests stiff, noncompressible arteries that make the test unreliable.

How do you calculate the ABI?

Divide the higher of the two ankle pressures in each leg (dorsalis pedis or posterior tibial) by the higher of the two arm pressures. For example, an ankle pressure of 110 mmHg and an arm pressure of 90 mmHg give 110 ÷ 90 = 1.22, which is normal.

What ABI is considered severe?

0.40 or less on the ACC/AHA scale, or below 0.50 on the scale many vascular and wound-care clinics use. Very low values, especially with rest pain or wounds that will not heal, need urgent assessment by a vascular specialist.

Why can the ABI be falsely high?

Calcified arteries, common in diabetes, chronic kidney disease and older age, resist the cuff, so it takes more pressure to close them. The ankle reading and the ABI then look normal or above 1.40 even when blood flow is reduced. A toe-brachial index avoids this because toe arteries rarely calcify.

Which arm pressure should I use for the ABI?

Measure both arms and use the higher systolic pressure for both legs. A difference of 15 mmHg or more between arms is worth telling your doctor about, because it can point to a narrowed artery on the lower side.

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This calculator interprets ankle and arm pressures measured by a trained clinician; it does not diagnose peripheral artery disease. Leg pain at rest, a cold or pale foot, or a wound that will not heal needs prompt medical care.