What this calculator does
Ankle-brachial index (ABI) works out peripheral artery disease screening ratio of ankle to arm blood pressure. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaABI (per leg) = ankle systolic pressure / higher arm systolic pressure
The inputs explained
| Field | What to enter |
|---|---|
| Right arm systolic pressure (mmHg) | A number, measured in mmHg. Starts at 120. |
| Left arm systolic pressure (mmHg) | A number, measured in mmHg. Starts at 120. |
| Right ankle systolic pressure (mmHg) | A number, measured in mmHg. Starts at 120. |
| Left ankle systolic pressure (mmHg) | A number, measured in mmHg. Starts at 120. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with right arm systolic pressure
Every other input is held at the calculator’s starting values while right arm systolic pressure varies. Select any row to load that scenario into the calculator.
How the answer changes with right arm systolic pressure
| Right arm systolic pressure (mmHg) | Lower-leg ABI (worse side) | Right ABI | Left ABI |
|---|---|---|---|
| 60 | 1.00 (Normal) | 1.00 (Normal) | 1.00 (Normal) |
| 90 | 1.00 (Normal) | 1.00 (Normal) | 1.00 (Normal) |
| 120 | 1.00 (Normal) | 1.00 (Normal) | 1.00 (Normal) |
| 180 | 0.67 (Mild to moderate PAD) | 0.67 (Mild to moderate PAD) | 0.67 (Mild to moderate PAD) |
| 240 | 0.50 (Mild to moderate PAD) | 0.50 (Mild to moderate PAD) | 0.50 (Mild to moderate PAD) |
| 360 | 0.33 (Severe PAD) | 0.33 (Severe PAD) | 0.33 (Severe PAD) |