ABI Calculator — Ankle-Brachial Index
Enter ankle and arm systolic pressures to get your per-leg ABI with standard interpretation ranges. Free, instant, and 100% private — everything runs in your browser.
Calculate your ABI
Measure systolic pressure (mmHg) at rest with a Doppler or automated device, then enter the values. The calculator automatically uses the highest ankle pressure per leg and the highest arm pressure — exactly like the standard ABI protocol.
Right leg — ankle
Left leg — ankle
Right arm — brachial
Left arm — brachial
ABI interpretation ranges
Standard ABI categories (ACC/AHA guidance). The calculator assigns each leg to one of these ranges automatically.
| ABI range | Category | What it generally means (educational) |
|---|---|---|
| > 1.40 | Noncompressible | Arteries may be stiff or calcified, so the cuff reading is unreliable. Clinicians often switch to the toe-brachial index (TBI) instead. |
| 1.00 – 1.40 | Normal | Ankle pressure keeps up with arm pressure — the expected screening result. |
| 0.91 – 0.99 | Borderline | Slightly low; often re-measured later or monitored, especially with risk factors. |
| 0.71 – 0.90 | Mild PAD range | Consistent with mild peripheral artery disease in screening terms; worth discussing with a clinician. |
| 0.41 – 0.70 | Moderate PAD range | Consistent with moderate peripheral artery disease in screening terms; clinical follow-up is typical. |
| ≤ 0.40 | Severe PAD range | Consistent with severe disease in screening terms; prompt clinical evaluation is typical. |
General next steps (information only, not medical advice)
- Discuss any borderline or abnormal value with a clinician — they may repeat the test, ask about leg symptoms (e.g. cramping when walking), and review your history.
- Know the common risk factors discussed in vascular guidance: smoking, diabetes, high blood pressure, high cholesterol, and older age.
- General vessel-friendly habits widely recommended by heart associations: don't smoke, stay physically active, and keep blood pressure, cholesterol, and blood sugar in check — as advised by your own clinician.
- Don't self-diagnose or change medication based on a calculator result.
Scope boundary: ABI vs toe-brachial index (TBI)
This tool computes the ankle-brachial index only. It does not compute the toe-brachial index (TBI), which compares toe pressure to arm pressure and needs a small toe cuff plus photoplethysmography — a different measurement setup. TBI matters mainly as the fallback when ABI is noncompressible (> 1.40), because toe arteries calcify less often than ankle arteries. If your result is above 1.40, the honest next step is a clinical TBI measurement, not a different online calculator.
How the calculation works
- Per leg, keep the higher ankle pressure: max(dorsalis pedis, posterior tibial).
- Keep the higher arm pressure: max(left brachial, right brachial) — used as the denominator for both legs.
- Divide: ABI = anklemax ÷ brachialmax, rounded to 2 decimals.
- Classify each leg into the standard range table above.
Because ABI is a ratio of two pressures, the mmHg units cancel out — the result is a unitless number, typically between 0.3 and 1.6.
Frequently asked questions
What is the ankle-brachial index (ABI)?
The ankle-brachial index (ABI) is a simple, non-invasive screening measurement that compares blood pressure at the ankle with blood pressure in the arm. A lower ankle pressure relative to the arm can suggest narrowed arteries in the legs, which is why ABI is commonly used as a screening step for peripheral artery disease (PAD). This page is educational only and cannot diagnose any condition.
How is ABI calculated? What is the ABI formula?
ABI is calculated per leg with the formula: ABI = (highest ankle systolic pressure) / (highest brachial systolic pressure). For each leg, take the higher of the dorsalis pedis and posterior tibial systolic pressures as the ankle value, and take the higher of the left and right arm brachial systolic pressures as the arm value. Example: ankle pressures of 120 mmHg (DP) and 118 mmHg (PT), with the highest arm pressure 120 mmHg, give ABI = 120 / 120 = 1.00.
What is a normal ABI range?
A normal ABI is 1.00 to 1.40. Values of 0.91 to 0.99 are considered borderline, and values of 0.90 or below are considered abnormal and are further grouped as mild (0.71-0.90), moderate (0.41-0.70), or severe (0.40 or below) peripheral artery disease ranges. An ABI above 1.40 is noncompressible, which usually means the arteries are stiff or calcified and the result is unreliable.
Which ankle pressure is used — dorsalis pedis or posterior tibial?
Both are measured and the higher of the two is used for each leg. Standard ABI protocol measures systolic pressure at the dorsalis pedis (top of the foot) and the posterior tibial (behind the inner ankle) arteries on each leg, then keeps the higher value per leg. This calculator does that automatically when you enter all four ankle pressures.
Which arm pressure is used in the ABI calculation?
The higher of the two brachial (upper arm) systolic pressures is used as the denominator for both legs. Enter the left and right arm pressures and this calculator picks the higher one automatically.
What does an ABI above 1.40 mean?
An ABI above 1.40 is called noncompressible. It usually means the leg arteries are stiff or calcified (common in diabetes or advanced kidney disease) so the blood pressure cuff cannot compress them properly, making the ABI unreliable. In that situation clinicians often measure the toe-brachial index (TBI) instead, because toe arteries calcify less often.
What is the difference between ABI and toe-brachial index (TBI)?
ABI compares ankle pressure to arm pressure, while the toe-brachial index (TBI) compares toe pressure to arm pressure. TBI is the usual fallback when ABI is noncompressible (above 1.40) because small toe arteries are less affected by calcification. This calculator computes ABI only; it does not compute TBI because toe pressures need a different measurement setup.
What do borderline or abnormal ABI results mean, and what are the general next steps?
Borderline (0.91-0.99) or abnormal (0.90 or below) ABI values suggest the result is worth discussing with a clinician, who may repeat the measurement, ask about symptoms such as leg pain when walking, review risk factors like smoking, diabetes, high blood pressure and cholesterol, or order further vascular testing. General, widely recommended heart-and-vessel habits include not smoking, staying active, and managing blood pressure, cholesterol and blood sugar — but only a qualified professional can interpret your result in context.
Why does the calculator ask for both legs?
ABI is calculated separately for each leg because peripheral artery disease can affect one leg more than the other. Comparing both legs also helps spot asymmetry, which clinicians consider informative. Enter all four ankle pressures (dorsalis pedis and posterior tibial on each leg) plus both arm pressures for a complete per-leg result.
Can this calculator diagnose peripheral artery disease?
No. This is an educational calculator, not a medical device and not a diagnosis. ABI categories describe ranges used in clinical screening, but a real assessment also considers symptoms, medical history, physical examination and sometimes imaging. Always discuss results with a qualified healthcare professional.
What units does the ABI calculator use?
Millimeters of mercury (mmHg), the standard unit for blood pressure. Because ABI is a ratio of two pressures, the units cancel out — the result is a plain number with no unit, typically between 0.3 and 1.6.
Is my health data sent anywhere when I use this calculator?
No. This calculator runs entirely in your browser using JavaScript. The pressures you enter are never uploaded, stored on a server, or shared — there are no network requests at all. Closing the tab removes everything.
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