Goniometer
Measure joint range of motion with your phone
Hold or strap the phone flat against the part that moves, lined up with it: the forearm for the elbow, the shin for the knee. Keep the rest of the body still.
The sensor measures movement that tilts the phone. For a movement parallel to the floor, lie on your side so it becomes an up-and-down movement, or enter a value instead.
Range so far
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Hold the starting position still, then record it.
For tracking your own progress. A phone reading is not a clinical measurement: don't use it to diagnose a condition or decide on treatment.
Log
Stays on this device
Nothing recorded yet.
About this tool
Track how far a joint moves. Rest your phone on the moving limb to measure a range of motion, or enter a reading from a physical goniometer, then compare left and right in a log that stays on your device.
How the goniometer works
A phone held against a limb tilts with it, so its tilt sensor can stand in for the moving arm of a goniometer. The page records the phone’s angle at the start of a movement and again at the end; the range of motion is the difference between the two.
Taking a reading
- Choose the joint, the movement and the side.
- Hold or strap the phone flat along the part that moves, such as the forearm for the elbow or the shin for the knee, and keep the rest of the body still.
- Hold the starting position and record it, move to the end of the range, hold still and record the end.
- The reading goes into a log on this device. With both sides recorded, the page shows the difference between left and right, and you can download the log as a CSV.
What it can and cannot measure
The sensor detects movement that tilts the phone up or down. A movement parallel to the floor, such as turning the forearm or swinging an arm sideways while standing, barely tilts it; lie on your side so the movement becomes vertical, or measure with a physical goniometer and enter the value by hand.
Readings depend on positioning: a phone that slips on the skin, a start position that changes from day to day or a body that moves along with the joint all change the number. Use the same position every time and compare like with like. The page shows no “normal” ranges on purpose, because published norms vary with the method and the source, and only a clinician can say what a measurement means for you.
Frequently asked questions
What is a goniometer used for?
A goniometer measures the angle a joint moves through, called its range of motion. Physiotherapists, occupational therapists and doctors use one to record how far a knee bends or an arm lifts, and to track changes over time, for example during rehabilitation after an injury or an operation.
This page uses your phone’s motion sensor to measure a range of motion and keeps a left-and-right log on your device. It is for tracking your own progress, not a clinical measurement.
What are the parts of a goniometer?
A universal goniometer has three parts. The fulcrum, or axis, is the pivot with the degree scale, placed over the joint. The stationary arm, also called the proximal arm, lines up with the body part that stays still. The moving arm, or distal arm, lines up with the part that moves and points to the reading.
When you measure with a phone, the phone takes the place of the moving arm: it measures how far the limb it rests on tilts between the start and the end of the movement.
How do you use a goniometer?
Start with the joint in its starting position and the rest of the body supported and still. Place the fulcrum over the joint’s axis of movement, line the stationary arm up with the segment that stays still and the moving arm with the segment that moves, and note the starting angle.
Then move the joint to the end of its range, realign the moving arm without shifting the fulcrum, and read the angle again. The difference is the range of motion. Use the same position every time and compare with the other side, because small changes in position change the reading.
How do you measure knee flexion with a goniometer?
Lie on your back with the leg straight. Place the fulcrum over the outside of the knee, at the lateral epicondyle of the femur. Point the stationary arm along the thigh toward the greater trochanter at the side of the hip, and the moving arm along the lower leg toward the lateral malleolus, the bony bump on the outside of the ankle.
Slide the heel toward the buttock to bend the knee as far as it goes, keep both arms aligned, and read the angle. With a phone, hold or strap it flat along the shin, record the start with the leg straight and the end at full bend. A phone reading is for tracking your own progress, not for diagnosis.
About these measurements
Readings are estimates taken from rendered pixels and consumer device sensors. Do not rely on them for structural engineering, surveying, manufacturing inspection, navigation, or medical decisions. Check anything safety-critical with a calibrated instrument.
All processing happens in your browser. No image, camera frame or sensor reading is ever uploaded.
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