Our ABI Calculator lets you perform an accurate ABI calculation (Ankle Brachial Index) online using your arm and ankle blood pressure values. The ABI is the ankle systolic pressure ÷ highest brachial systolic pressure; clinicians use it to screen for PAD and to grade disease severity. A normal resting ABI is 1.00–1.40, 0.91–0.99 is borderline, ≤0.90 is abnormal (PAD), and >1.40 suggests non-compressible arteries that need follow-up testing (often a toe–brachial index, TBI).
ABI Calculator (Ankle Brachial Index)
Calculate the Ankle-Brachial Index by entering the highest arm blood pressure and ankle pressures for each leg.
What is the ankle–brachial index?
- ABI compares leg to arm blood pressure. It’s a quick, non-invasive test that helps detect PAD, a condition where narrowed leg arteries reduce blood flow.
- ABI is widely recommended in people with PAD symptoms or risk factors (smoking, diabetes, high cholesterol, high blood pressure, age).
ABI Calculation Formula (How to calculate ABI step-by-step)
- Measure brachial pressures in both arms; keep the higher value.
- Measure ankle systolic pressure in each leg (use the higher of dorsalis pedis or posterior tibial for that leg).
- Right ABI = highest right-ankle ÷ highest arm; Left ABI = highest left-ankle ÷ highest arm.
Worked example: highest right ankle = 139 mmHg; highest arm = 126 mmHg → ABI = 139/126 = 1.10 (normal).
ABI interpretation (resting)
| ABI range | Category | Typical note |
|---|---|---|
| > 1.40 | Non-compressible | Calcified/stiff arteries; measure TBI |
| 1.00–1.40 | Normal | No PAD by ABI |
| 0.91–0.99 | Borderline | Consider exercise ABI if symptoms |
| ≤ 0.90 | Abnormal (PAD) | Lower values = worse PAD severity |
These cutoffs reflect contemporary ACC/AHA guidance; many labs further subclassify ≤0.90 into mild–moderate (0.41–0.90) and severe (<0.40).
When ABI is unreliable and when to use the Toe–Brachial Index (TBI)
- ABI > 1.40 or long-standing diabetes/CKD can mean stiff, non-compressible ankle arteries and falsely high ABI. In this setting, guidelines advise TBI to diagnose PAD.
- Studies commonly use TBI < 0.70 as abnormal.
The ankle–brachial test: what happens
- A technician places cuffs on both arms and ankles and uses a Doppler probe; the test is fast and safe.
- If your resting ABI is normal but you have exertional leg symptoms, an exercise ABI (treadmill) can unmask PAD.
Normal ABI index (values & meaning)
- Normal resting ABI is 1.00–1.40; 0.91–0.99 is borderline; ≤0.90 is PAD; >1.40 suggests non-compressible vessels.
Ankle–brachial test vs ABI calculator
- The ankle brachial test is a clinic procedure; an abi calculator lets clinicians and learners compute the ratio once pressures are measured. Both rely on the same formula and interpretation ranges.
Toe–brachial index (TBI)
- Use TBI when ABI > 1.40 or arteries are non-compressible; TBI < 0.70 supports PAD.
FAQ — “People also ask” about an ABI calculator
When is the ABI unreliable, and when should you use the Toe–Brachial Index (TBI)?
If your ABI > 1.40 or you have long-standing diabetes/CKD, ankle arteries can be non-compressible, producing falsely high ABI results. Current ACC/AHA PAD guidelines say to perform toe pressures/TBI (with waveforms) when the resting ABI is non-compressible. TBI is also useful when symptoms suggest PAD but ABI seems “normal” due to arterial calcification.
What TBI value is abnormal?
Many clinical sources and public-health guidance treat TBI < 0.70 as abnormal and supportive of PAD.
What happens during the ankle–brachial test?
A clinician places blood-pressure cuffs on your arms and ankles and uses a Doppler probe to measure systolic pressures. The ABI is the ankle systolic ÷ arm systolic; the test is quick, safe, and non-invasive. If resting ABI is normal or borderline but you still have exertional leg symptoms, an exercise (treadmill) ABI can unmask PAD.
What are normal ABI index values (and what do they mean)?
Standard reporting categories are: normal 1.00–1.40, borderline 0.91–0.99, abnormal ≤ 0.90 (PAD), and non-compressible > 1.40. Some references also note severe PAD around ABI < 0.40.
Ankle–brachial test vs ABI calculator — what’s the difference?
The ankle brachial test is the clinic procedure that measures the pressures in your arms and ankles using cuffs and Doppler. An ABI calculator (like yours) then computes the ratio and labels the result with guideline ranges (normal, borderline, abnormal, non-compressible). Both use the same formula and interpretation.
How to calculate ABI?
Measure systolic pressures in both arms and keep the higher value. For each leg, measure both ankle arteries (dorsalis pedis and posterior tibial) and keep the higher value for that leg. ABI = ankle ÷ highest arm, calculated separately for right and left.
How to calculate ABI index / ABI ratio?
It’s the same calculation: ankle systolic ÷ highest brachial systolic. Using the higher ankle artery for each leg and the higher of the two arms prevents falsely low or high results.
How do you calculate ABI for a patient step-by-step?
- Measure both arms → keep the higher arm. 2) Measure each ankle (DP and PT) → keep the higher ankle reading per leg. 3) Compute Right ABI and Left ABI with the same highest arm value. 4) Interpret using standard ranges.
How is ABI calculated — example?
If right ankle = 139 mmHg and the highest arm = 126 mmHg, ABI = 139/126 = 1.10, which is normal. (Any equivalent ankle/arm pair works the same way.) .
What is a normal ABI index?
Report as: normal 1.00–1.40, borderline 0.91–0.99, abnormal ≤ 0.90 (PAD), non-compressible > 1.40. Use exercise ABI if symptoms persist with normal/borderline results.
What if my ABI > 1.40?
That suggests non-compressible arteries (often due to calcification), so the resting ABI can be falsely high. Guidelines advise TBI with waveforms to evaluate for PAD.
Is ABI accurate in diabetes or kidney disease?
ABI can be falsely elevated because medial arterial calcification makes ankle arteries hard to compress. In these settings, TBI (toe-pressure index) is recommended to assess perfusion.
When should I get an ABI test?
Get tested if you have leg pain when walking, non-healing foot wounds, or risk factors like smoking, diabetes, high cholesterol, or high blood pressure—or if your clinician suspects PAD. If resting ABI is normal/borderline but symptoms persist, ask about exercise ABI.
What does a low ABI mean for heart and stroke risk?
A low ABI (≤ 0.90) indicates PAD and is associated with higher cardiovascular risk. Managing risk factors and receiving guideline-directed care can lower event risk. Patient resources from major centers explain the link and next steps.
Can I measure ABI at home?
Accurate ABI typically needs proper cuffs and a Doppler in a clinic or vascular lab. Home calculation tools can help you interpret numbers once pressures are measured, but they don’t replace a medical assessment.
Sources (key, recent, and guideline-based)
- 2024 ACC/AHA PAD Guideline slide set — ABI categories; when to use TBI; exercise ABI if normal/borderline. www.heart.org
- SVS/SIR/VESS 2024 pocket guide — Standard reporting: normal 1.00–1.40, borderline 0.91–0.99, abnormal ≤ 0.90, non-compressible > 1.40. xareltohcp.com
- Johns Hopkins — Patient explanation of the ABI test and how it’s performed. Hopkins Medicine
- AAFP review — When to do exercise ABI with normal resting ABI but exertional symptoms. American Academy of Family Physicians
- NHLBI (NIH) — Public-health guidance noting TBI < 0.7 as abnormal; ABI thresholds. NHLBI, NIH