How this calculator works
For each leg, divide the higher dorsalis pedis or posterior tibial systolic pressure by the higher brachial pressure from either arm. The 2024 AHA/ACC guideline reports ABI ≤0.90 as abnormal, 0.91 to 0.99 as borderline, 1.00 to 1.40 as normal and above 1.40 as noncompressible. For unrounded ratios this page treats values above 0.90 but below 1.00 as borderline. Calcified arteries may make ABI misleading. The result is an estimate for information only and is not medical advice.
Formula
Right ABI = higher right ankle SBP / higher arm SBP. Left ABI uses the corresponding left ankle pressure and the same arm denominator.
Worked example
With arm pressure 120 mmHg, right ankle 108 gives ABI 0.90 (abnormal); left ankle 132 gives 1.10 (normal).
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Frequently asked questions
Which arm do I use?
Use the higher measured brachial systolic pressure.
Is a normal ABI enough to exclude disease?
No. Symptoms, exercise testing and other vascular measurements can still matter.
What does a value above 1.40 mean?
It is classified as noncompressible and may require other assessment, such as toe pressures.