The Achilles tendon can be measured in several ways depending on what you’re trying to learn: its thickness (using ultrasound or MRI), its flexibility (using range-of-motion tests), or its functional strength (using simple physical tests you can do at home or in a clinic). A healthy Achilles tendon measures about 4.9 mm thick at the midportion, and values above roughly 7 mm at that location often signal a problem.
Measuring Tendon Thickness With Ultrasound
Ultrasound is the most common clinical tool for measuring how thick the Achilles tendon is. During the exam, you lie face down on a table with your feet hanging off the edge and your ankle slightly bent upward. The examiner runs the probe along the tendon lengthwise (longitudinally), which gives the clearest view of both the tendon’s thickness and how it connects to the heel bone.
Thickness is measured at two key spots: 4 centimeters and 6 centimeters above where the tendon inserts into the calcaneus (heel bone). In healthy people, the midportion of the tendon has a median thickness of 4.9 mm, with a normal range of 3.8 to 6.9 mm. The insertional region, closer to the heel, is thinner: about 3.7 mm on average, with a normal range of 2.8 to 4.8 mm. A large international study found that 73% of patients with Achilles tendinopathy had thickness values above these normal ranges. On average, tendons with midportion tendinopathy were 2.7 mm thicker than healthy tendons, and insertional tendinopathy added about 1.4 mm.
Longitudinal measurements (probe running along the length of the tendon) are preferred over cross-sectional slices because they let the examiner confirm exactly how far from the heel bone they’re measuring. Without that reference point, it’s easy to take readings at the wrong spot.
When MRI Is Used Instead
MRI provides a more detailed picture than ultrasound and is better at detecting partial tears inside the tendon. A normal Achilles tendon appears very dark on standard MRI sequences. When the tendon is damaged, areas of brighter signal show up, indicating fluid, tearing, or degeneration. Thin bright lines between the tendon’s subtendons are normal and can be mistaken for tears by an untrained eye, so interpretation matters as much as the image itself.
MRI is typically reserved for cases where ultrasound results are unclear, a partial tear is suspected, or surgery is being considered. It’s not a first-line measurement tool for routine tendon assessment.
The Thompson Test for Rupture
If the concern is whether the tendon is completely torn, the Thompson test is a quick hands-on check that doesn’t require any equipment. You lie face down with your feet hanging off the edge of a table. The examiner squeezes your calf muscle firmly. In a healthy tendon, this squeeze automatically pulls the foot downward (like pressing a gas pedal). If the foot doesn’t move at all, the tendon is likely ruptured.
The examiner will often test both legs to compare how much the foot moves on each side. A “positive” Thompson test (no foot movement) points toward a rupture. A “negative” result (normal foot movement) suggests the tendon is intact. This test checks structural continuity, not thickness or flexibility, so it answers a very specific question: is the tendon still in one piece?
Measuring Flexibility With the Wall Lunge Test
The weight-bearing lunge test is a simple, reliable way to measure ankle dorsiflexion, which reflects how flexible your Achilles tendon and calf complex are. Stand facing a wall with one foot forward. Keep your front heel flat on the ground and bend your knee toward the wall until your knee touches it. Slide your foot back gradually until you find the maximum distance where your knee can still reach the wall without your heel lifting.
The measurement is the distance in millimeters from your big toe to the wall. In people with healthy ankles, average scores are around 116 mm (roughly 4.5 inches). Those with ankle problems or stiff Achilles tendons score significantly lower, averaging closer to 57 mm. You can track this number over time to monitor progress during rehabilitation. A difference of more than about 1.5 cm between your two legs is generally considered meaningful.
Testing Functional Strength With Heel Raises
The single-leg heel-rise test measures how well the tendon performs under load. Stand on one foot on a flat surface (or on the edge of a step for a greater challenge) and rise up onto your toes as many times as you can at a steady pace. Count the repetitions until you can no longer reach full height or you need to stop.
Healthy men typically complete about 24 repetitions, while healthy women average around 21. These numbers decline with age, though interestingly, women over 60 tend to outperform men of the same age on this test. If you’re recovering from Achilles tendinopathy, comparing your count to these norms and to your uninjured side gives you a practical gauge of how much strength the tendon has recovered.
Measuring Range of Motion With a Goniometer
A goniometer is a protractor-like tool that clinicians use to measure joint angles in degrees. For the ankle, the center pivot is placed over the joint’s axis of rotation, found by feeling the bony bumps on either side of the ankle (the medial and lateral malleoli). One arm of the goniometer aligns with the outer leg bone (fibula), and the other aligns with the bottom of the foot, using either the heel or the base of the little toe as a reference.
Normal ankle dorsiflexion (pulling the foot upward toward the shin) is roughly 10 to 20 degrees. A restricted range can indicate tightness in the Achilles tendon or calf muscles. This measurement is most useful when done by a trained clinician who can ensure consistent landmark placement, since even small errors in positioning change the reading.
Tracking Symptoms With the VISA-A Score
The VISA-A questionnaire is a standardized way to measure how much Achilles tendinopathy affects your daily life and activity. It scores from 0 to 100, where 100 means no symptoms at all. Healthy individuals typically score between 96 and 100. A score below 60 is common in people actively dealing with tendinopathy, and scores around 24 represent the severe end of the spectrum.
The questionnaire asks about pain during specific activities like walking, going downstairs, and exercising. It’s useful for tracking your progress over weeks and months of treatment. Reaching a score above 90 is considered full recovery. Because it captures the real-world impact of the condition, not just what an image shows, many clinicians consider it one of the most practical measurement tools available for Achilles tendon problems.
Measuring Tendon Length
Total Achilles tendon length is measured from the point where the calf muscle (medial head of the gastrocnemius) transitions into tendon tissue down to the bottom of the heel pad. This is done with ultrasound by identifying the musculotendinous junction, the spot where muscle fibers end and the tendon begins, and tracing down to the heel. Tendon length varies considerably between individuals and can influence injury risk, but it’s primarily a research measurement rather than something tracked in routine clinical care.