Leg length is measured from a bony point on the front of your pelvis to the bony bump on the inside of your ankle, using a simple tape measure. This “true” leg length measurement is the standard method used in clinical settings, and you can approximate it at home with a helper. The distance typically falls around 78 to 93 centimeters (roughly 31 to 37 inches) for most adults, though what matters more than the raw number is whether your two legs match.
True Leg Length: The Standard Method
The clinical gold standard uses two bony landmarks you can feel through the skin. The starting point is the anterior superior iliac spine, or ASIS, which is the bony point at the very front of each hip bone. If you place your hands on your hips and slide your fingers forward and down, you’ll feel a firm, protruding knob on each side. The endpoint is the medial malleolus, the round bone that sticks out on the inside of your ankle.
To take the measurement, lie flat on your back on a firm surface with your legs extended straight and parallel. Have a helper place one end of a flexible tape measure on the ASIS and run it down the inside of your leg to the tip of the medial malleolus. Record the measurement in centimeters or millimeters, then repeat on the other side. The difference between the two numbers is your leg length discrepancy.
Positioning matters. Your pelvis should be square, not tilted, and both legs should be in the same position. Even a slight bend at the knee or rotation at the hip can throw off the reading by several millimeters. It helps to have your helper gently straighten both legs and align them symmetrically before measuring.
How Accurate Is a Tape Measure?
Tape measurement is surprisingly reliable when done carefully. Compared to CT scanograms (the imaging gold standard), tape measurements show good accuracy, with studies reporting agreement coefficients around 0.80 to 0.85. The average difference between tape and CT readings is about 2 millimeters, though individual measurements can vary by up to 7 millimeters from the CT result.
The biggest source of error is inconsistent landmark identification. The ASIS can be harder to locate on people with more soft tissue over the hip bones, and pressing the tape into skin versus holding it loosely changes the reading. For the most consistent results, take three measurements on each side and use the average.
The Block Test: A Functional Alternative
If you’re checking for a discrepancy while standing, the block test offers a practical approach. Stand barefoot on a hard floor and have someone observe whether your pelvis looks level from behind. Then place thin boards or shims (measured with known thicknesses) under the foot of the shorter leg until the pelvis appears level. The total thickness of the blocks equals your functional discrepancy.
This method captures something the tape measure misses. A tape measures bone length only, but the block test reflects everything that affects your standing alignment: bone length, joint angles, pelvic tilt, and spinal curvature combined. A discrepancy that shows up on the block test but not on tape measurement suggests the difference comes from soft tissue or joint mechanics rather than bone structure.
Imaging Methods for Precise Measurement
When precision matters, such as before surgery, doctors use imaging. The most common options are full-length standing X-rays and CT scanograms. Both measure bone segments individually (femur and tibia) and add them together, which also reveals where the discrepancy originates.
A comparison study of 51 patients found no significant differences in limb length measurements between CT scans, full-length standing X-rays, and newer 3D radiography systems. All three methods produced mean leg lengths within 2 to 5 millimeters of each other. The 3D biplanar technique showed the best agreement between different readers, meaning two radiologists measuring the same image got nearly identical results. For most people, though, imaging is only necessary if a clinical measurement suggests a meaningful discrepancy or if surgery is being planned.
Leg Length vs. Inseam
A clothing inseam measures from your crotch to the floor or hem, which captures only part of the leg and depends heavily on where the crotch point sits. It tells you nothing useful about skeletal leg length. An anatomical leg length measurement runs from the pelvis to the ankle and reflects actual bone structure. If you’re measuring for medical purposes, always use the ASIS-to-ankle method, not your pants size.
When a Difference Actually Matters
Almost everyone has some degree of leg length difference. The question is how much is enough to cause problems. The best available evidence suggests that a discrepancy under about 20 millimeters (roughly three-quarters of an inch) is not clinically significant for most people under normal activity levels. If you’re doing heavy or repetitive loading, like distance running, the threshold may be slightly lower, around 15 millimeters.
Below these thresholds, your body compensates naturally through subtle adjustments in pelvic tilt, knee bend, and foot posture. Above them, discrepancies are more likely to contribute to lower back pain, hip arthritis, or knee problems over time.
What Happens After You Find a Discrepancy
For discrepancies that are noticeable but modest, a shoe lift is the first-line approach. It’s inexpensive, noninvasive, and easy to try or stop. Shoe lifts can be placed inside the shoe (for differences up to about 10 millimeters) or built into the sole by a cobbler for larger corrections. Research shows they can reduce pain and improve function in people with lower back pain, hip arthritis, or knee arthritis related to uneven leg length.
In children who are still growing and have a discrepancy expected to reach 2 to 5 centimeters at maturity, a surgical technique called epiphysiodesis can slow growth on the longer leg by temporarily or permanently closing the growth plate. This approach works only while growth plates are still open, so timing is critical. For larger discrepancies, surgical lengthening of the shorter leg becomes an option, though it involves a significantly longer recovery.