How to measure ankle range of motion
Clinical guide · Updated July 2026
To measure ankle dorsiflexion with a goniometer, position the patient with the knee bent and the foot in neutral, center the fulcrum below the lateral malleolus, align the stationary arm with the fibula and the moving arm parallel to the fifth metatarsal, then pull the foot up toward the shin and read the angle. Normal ankle ROM is about 20° dorsiflexion and 50° plantarflexion (AAOS). The steps, landmarks, and reliability evidence are below.
Normal ankle range of motion
| Movement | Normal ROM |
|---|---|
| Dorsiflexion | 20° |
| Plantarflexion | 50° |
| Inversion | 35° |
| Eversion | 15° |
See the full normal range of motion chart for every joint. The Goniometer app guides ankle dorsiflexion and plantarflexion with animated placement.
What you need
- A universal goniometer, digital goniometer, or a smartphone goniometer app.
- A position where the knee can be bent to relax the calf and the foot is free to move.
- Reference to the landmarks: the lateral malleolus, the fibula (toward the fibular head), and the lateral border of the foot (fifth metatarsal).
How to measure ankle dorsiflexion, step by step
- Position the patient. Seated or supine with the knee bent about 90° to relax the calf, foot in neutral with the sole roughly perpendicular to the shin — this is the 0° starting position.
- Find the landmarks. Locate the lateral malleolus, the fibula toward the fibular head, and the lateral border of the foot along the fifth metatarsal.
- Center the fulcrum. Place the goniometer axis just below the lateral malleolus.
- Align the arms. Line the stationary arm along the fibula and the moving arm parallel to the lateral border of the foot.
- Move to end range. Pull the foot up toward the shin (dorsiflexion) until it stops, without letting the foot roll in or out.
- Read and record. Read the angle at end range and note the side (L/R) and knee position.
Ankle plantarflexion
Keep the same position and point the foot down and away from the shin; normal is about 50°. Inversion (about 35°) and eversion (about 15°) turn the sole inward and outward and are measured from behind the heel.
Getting a reliable measurement
Ankle goniometry is moderately reliable, and best with one examiner. Elveru and colleagues found ankle and subtalar measurements moderately reliable when taken by the same therapist over a short period; between different therapists, only ankle plantarflexion reached good reliability. Four habits keep readings repeatable:
- Bend the knee to relax the calf for dorsiflexion, and keep the knee position identical across visits.
- Control subtalar motion — don’t let the foot roll in or out, which adds apparent range.
- Read at a stable end range, not mid-motion, and to the whole degree.
- Use one examiner for progress tracking. Compare a patient’s ankle to their own earlier measurement, taken the same way.
Measuring ankle ROM with an iPhone
A smartphone goniometer app replaces the two-armed goniometer with the phone’s gravity-referenced motion sensor: lay the phone along the foot, set zero, and the change in tilt as the ankle moves is the joint angle. Peer-reviewed research finds smartphone measurement valid and reliable for ankle ROM, comparable to a universal goniometer — see the accuracy evidence. A 2021 study found good reliability for weight-bearing ankle dorsiflexion measured with a smartphone goniometer app (Zunko & Vauhnik).
Measure the ankle on your iPhone. Goniometer shows animated placement for ankle dorsiflexion and plantarflexion, with the AAOS normal range beside every reading — free to measure. Download Goniometer on the App Store.
Frequently asked questions
What is normal ankle range of motion?
About 20° dorsiflexion, 50° plantarflexion, 35° inversion, and 15° eversion, per AAOS.
How do you measure ankle dorsiflexion with a goniometer?
With the knee bent, center the fulcrum below the lateral malleolus, align the stationary arm with the fibula and the moving arm parallel to the fifth metatarsal, pull the foot up toward the shin, and read the angle.
Why is the knee bent when measuring dorsiflexion?
Bending the knee relaxes the gastrocnemius (calf) muscle, which crosses the knee; a straight knee tightens it and limits dorsiflexion, changing the reading.
How reliable is ankle goniometry?
Moderately reliable, best with one examiner: Elveru et al. found ankle measurements moderately reliable within the same therapist, with only plantarflexion reliable between therapists.
Can you measure ankle range of motion with a phone?
Yes — a smartphone goniometer app reads the phone’s motion sensor and has shown validity and reliability comparable to a universal goniometer in peer-reviewed research.
References
- Norkin CC, White DJ. Measurement of Joint Motion: A Guide to Goniometry. 5th ed. Philadelphia: F.A. Davis; 2016.
- American Academy of Orthopaedic Surgeons. Joint Motion: Method of Measuring and Recording. Chicago: AAOS. Normative range-of-motion reference values, as used throughout the Goniometer app.
- Elveru RA, Rothstein JM, Lamb RL. Goniometric reliability in a clinical setting. Subtalar and ankle joint measurements. Physical Therapy. 1988;68(5):672–677. academic.oup.com/ptj/68/5/672
- Zunko H, Vauhnik R. Reliability of the weight-bearing ankle dorsiflexion range of motion measurement using a smartphone goniometer application. PeerJ. 2021;9:e11977. doi:10.7717/peerj.11977
- Keogh JWL, Cox A, Anderson S, et al. Reliability and validity of clinically accessible smartphone applications to measure joint range of motion: A systematic review. PLOS ONE. 2019;14(5):e0215806. doi:10.1371/journal.pone.0215806
Related guides
Goniometer is an educational and reference tool. It is not a medical device and is not intended for diagnosis or treatment decisions.