Calculate leg length discrepancy from true and apparent measurements
Enter the true and apparent lengths of both legs measured with a tape; see the difference, the shorter side and whether the two measurements agree.
True length (ASIS → medial malleolus)
Apparent length (umbilicus → medial malleolus) — optional
Difference
Enter the true length of both legs.
A screening method
Tape measurement carries an error of a few millimetres. A definitive assessment is made with imaging; the lift decision and amount belong to the clinician.
Who are you?
Run this measurement automatically from a scan in your clinic
In a 30-minute demo we'll show the same calculation on a 3D scan, with your own case. Your result is added to the form automatically.
Result added to the form
No calculated result yet — you can still send the form.
Frequently asked questions
What is the difference between true and apparent leg length?
True length is the tape measurement from the anterior superior iliac spine (ASIS) to the medial malleolus and reflects bone length. Apparent length runs from the umbilicus to the medial malleolus and also includes functional factors such as pelvic obliquity and contractures. A mismatch between the two hints at whether a discrepancy is structural or functional.
How reliable is tape measurement?
The tape method is a practical screening method but carries a measurement error of a few millimetres. Imaging (for example a standing full-length lower-limb radiograph) is used for a definitive assessment. Having the same person measure in the same position and repeating it twice improves consistency.
How large a difference needs a lift?
A lift decision depends not only on the difference but on age, symptoms, whether the discrepancy is structural or functional, and gait. This tool does not recommend a lift amount; the decision belongs to the clinician.