# ABI Calculator (Ankle-Brachial Index)

URL: https://speedycalculator.com/calculators/health/abi/
Last updated: 2026-10-30

> The ankle-brachial index calculator divides the highest ankle systolic pressure on each leg by the highest arm pressure to screen for peripheral artery disease (PAD), and grades each leg from normal to severe.

## Inputs

- Left arm (brachial) systolic (mmHg)
- Right arm (brachial) systolic (mmHg)
- Left dorsalis pedis (mmHg)
- Left posterior tibial (mmHg)
- Right dorsalis pedis (mmHg)
- Right posterior tibial (mmHg)

## Results

- Left ABI
- Right ABI
- ABI (worse leg)

## Formula

```
ABI (each leg) = higher of dorsalis pedis and posterior tibial pressure ÷ higher of the two brachial pressures
> 1.40 non-compressible · 1.00–1.40 normal · 0.91–0.99 borderline · 0.41–0.90 mild to moderate PAD · ≤ 0.40 severe PAD
```

## Explanation

The ABI is a simple, painless test for narrowed leg arteries. A low ABI also predicts heart attack and stroke risk. Very high values usually mean stiff, calcified arteries, common in diabetes and kidney disease.

### How to use the ABI Calculator

- **Left arm (brachial) systolic**
- **Right arm (brachial) systolic**
- **Left dorsalis pedis**
- **Left posterior tibial**
- **Right dorsalis pedis**
- **Right posterior tibial**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

With the patient lying flat for 10 minutes, measure systolic pressure in both arms and at both ankle arteries on each leg with a Doppler probe. The worse leg determines the overall result.

### Inputs explained

FieldWhat to enterLeft arm (brachial) systolicIn mmHgRight arm (brachial) systolicIn mmHgLeft dorsalis pedisIn mmHgLeft posterior tibialIn mmHgRight dorsalis pedisIn mmHgRight posterior tibialIn mmHg

### What each result means

- **Left ABI** = max([Left dorsalis pedis], [Left posterior tibial])÷max([Left arm (brachial) systolic], [Right arm (brachial) systolic])
- **Right ABI** = max([Right dorsalis pedis], [Right posterior tibial])÷max([Left arm (brachial) systolic], [Right arm (brachial) systolic])
- **ABI (worse leg)** = min([Left ABI], [Right ABI])

### Example values

How the main result changes when **Left arm** changes and everything else stays at the example values above:

Left arm (brachial) systolic (mmHg)ABI (worse leg)650.8297.50.821300.81162.50.651950.542600.4
*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — Left arm (brachial) systolic: 130 mmHg; Right arm (brachial) systolic: 128 mmHg; Left dorsalis pedis: 120 mmHg; Left posterior tibial: 125 mmHg; Right dorsalis pedis: 105 mmHg; Right posterior tibial: 100 mmHg.

Results — Left ABI = 0.96; Right ABI = 0.81; **ABI (worse leg) = 0.81**.

## Key terms

- **PAD**: Peripheral artery disease.

## FAQ

**What is a normal ABI?**
1.00–1.40.

**What ABI means peripheral artery disease?**
0.90 or less.

**Why can the ABI be falsely normal or high?**
Calcified arteries in diabetes or kidney disease resist compression; a toe-brachial index helps.


## Sources

- [Aboyans V et al. Measurement and interpretation of the ankle-brachial index: AHA scientific statement. Circulation, 2012](https://pubmed.ncbi.nlm.nih.gov/23159553/)