ABPI Calculator (Ankle Brachial Pressure Index)

ABPI (ankle brachial pressure index) = the higher ankle systolic pressure in each leg ÷ the higher of the two arm systolic pressures. A resting ABPI of 1.00–1.40 is normal, 0.91–0.99 borderline, 0.90 or less abnormal and consistent with peripheral artery disease, and above 1.40 means the arteries are too stiff to read (2024 ACC/AHA guideline).

This ABPI calculator (also called an ABI calculator) gives a separate index for each leg, flags which leg sets the diagnosis and labels each value with the guideline band. It is written for nurses, doctors, podiatrists and students who have already taken the Doppler pressures.

How to use this calculator

1. Lay the patient flat and let them rest, as NICE CG147 recommends.
2. Measure the systolic pressure in both arms with a hand-held Doppler and an appropriately sized cuff.
3. At each ankle, measure the posterior tibial and dorsalis pedis pressures. Leave a box empty if a signal cannot be found.
4. Read the ABPI for each leg. The lower of the two is the one that matters for diagnosis.

The ABPI formula

Each leg is calculated on its own:

ABPI (leg) = highest ankle systolic pressure in that leg ÷ highest brachial systolic pressure (either arm)

This is the method in NICE CG147 recommendation 1.3.3, which says to "calculate the index in each leg by dividing the highest ankle pressure by the highest arm pressure". NICE also asks for the peroneal artery "where possible"; if you have a peroneal reading that is higher than the other two, use it in the posterior tibial box. The 2012 AHA scientific statement by Aboyans and colleagues uses the same rule, with both legs sharing one arm denominator. The result is reported to two decimal places, and this calculator classifies the rounded value.

ABPI ranges and what they mean

Resting ABPI categories from the 2024 ACC/AHA lower extremity PAD guideline:

For a noncompressible result the guideline moves to toe pressures, because the toe arteries are less often calcified. A toe-brachial index (TBI) of 0.70 or less is diagnostic of PAD, as the American Family Physician summary of the 2024 guideline notes. Older guidance sometimes used different cut-offs at the top end, so check the year of any chart you compare against.

Worked examples

Five sets of pressures run through the calculator's own functions.

In the claudication example, the higher arm pressure is 140 mmHg. The right leg's best ankle pressure gives 1.04, which is normal. The left leg's best ankle pressure is 102 mmHg, so 102 ÷ 140 = 0.73, which is abnormal and fits the left calf symptoms. The diabetes example shows why a high value is not reassuring: both legs read above 1.40, so the result cannot be used and toe pressures are needed.

Measuring the pressures well

Most wrong ABPI results come from technique rather than arithmetic. The NICE and AHA advice comes down to a few habits:

• Rest first, lie flat. Exercise or sitting up changes ankle pressures.
• Use the right cuff size. A cuff that is too small over-reads, especially on large or swollen ankles.
• Use a hand-held Doppler. NICE prefers manual Doppler readings to automated systems.
• Keep a fixed order. The AHA statement gives an example sequence: right arm, right posterior tibial, right dorsalis pedis, left posterior tibial, left dorsalis pedis, left arm. Use the same order for every patient.
• Recheck an arm difference. If the first and last arm readings differ by 10 mmHg or more, the AHA advice is to repeat the first arm at the end. The calculator flags a gap of 10 mmHg or more.

ABPI in diabetes and kidney disease

Calcified, stiff arteries are the main reason an ABPI misleads. NICE CG147 tells clinicians not to exclude PAD in people with diabetes based on a normal or raised ABPI alone, because hardening of the arteries can push the value up even when there is narrowing. In practice this means:

• a value above 1.40 should be treated as unreadable, not as excellent circulation;
• a normal value in a person with diabetes and foot ulceration, absent pulses or rest pain still needs further assessment;
• toe pressures or a toe-brachial index are the usual next step.

When resting ABPI is normal but symptoms are not

Some people only have reduced flow when the leg muscles demand more blood. The AHA statement says that when the resting ABI is above 0.90 but PAD is suspected, a post-exercise ABI or imaging can be used, and that a fall in ankle pressure of more than 30 mmHg or a fall in ABI of more than 20% after exercise may be considered a criterion for PAD. This calculator handles the resting index; enter the post-exercise pressures separately and compare.

ABPI and compression for leg ulcers

In UK community nursing the ABPI is often taken before compression bandaging for a venous leg ulcer, to make sure the arterial supply can tolerate it. Thresholds differ between guidelines. Weller and colleagues reviewed 13 international venous leg ulcer guidelines in 2019 and found no agreement on the ABPI range in which compression is safe, with the most disagreement between 0.6 and 0.8. This page therefore does not print a compression threshold: use your local tissue-viability or leg-ulcer pathway, and refer for vascular assessment when the result is low, unreadable or does not fit the clinical picture.

Common mistakes

• Using one arm only. The denominator is the higher of the two arm pressures.
• Averaging the two ankle pulses. Each leg uses its higher ankle pressure, not the mean.
• Reporting one number for both legs. Report each leg separately; the lower value guides diagnosis.
• Reading a high value as healthy. Above 1.40 means the test could not compress the artery.
• Mixing old and new bands. The 2024 guideline uses 0.91–0.99 for borderline and 1.00–1.40 for normal.

More clinical tools: QTc calculator, anion gap, BUN/creatinine ratio and A1C to average glucose.

For healthcare professionals and students only. The ABPI is one part of a vascular assessment. It does not diagnose the cause of leg pain or ulceration and this tool offers no medical advice. A cold, pale, painful or numb leg is an emergency. Patients should see their own clinician.

Frequently asked questions

Sources & method

• Gornik HL, Aronow HD, Goodney PP et al. (2024), Circulation — 2024 ACC/AHA/AACVPR/APMA/ABC/SCAI/SVM/SVN/SVS/SIR/VESS guideline for the management of lower extremity peripheral artery disease
• Arnold M (2025), American Family Physician — Management of lower extremity PAD: guidelines from the ACC/AHA (ABI categories, toe-brachial index ≤0.70)
• Aboyans V, Criqui MH et al. (2012), Circulation — Measurement and interpretation of the ankle-brachial index: an AHA scientific statement
• American Family Physician (2013) — AHA releases recommendations on ankle-brachial index measurement and interpretation (summary of Aboyans 2012)
• NICE CG147 — Peripheral arterial disease: diagnosis and management, recommendations 1.3.3–1.3.4
• Weller CD, Team V, Ivory JD, Crawford K, Gethin G (2019), International Wound Journal — ABPI reporting and compression recommendations in global venous leg ulcer guidelines: a scoping review

Results are estimates for general information. Found an error? It helps everyone — see our methodology.