CDC knee flexion and extension by age and sex, common reference values and how to measure them.
This page is a measurement reference for physical therapists, occupational therapists, students and other clinicians. Patients with joint pain or stiffness should be examined by a licensed clinician.
Knee range of motion values from the CDC Normal Joint Range of Motion Study (where it measured this joint), the most-quoted reference values, and our clinicians’ goniometry steps for each motion. All values are in degrees.
| Motion | AAOS reference value | VA rating schedule | CDC mean, women / men, 20–44 | CDC mean, women / men, 45–69 |
|---|---|---|---|---|
| Flexion | 135°[4] | 140°[5] | 141.9° / 137.7° | 137.8° / 132.9° |
| Extension | 0°[4] | 0°[5] | 1.6° / 1.0° | 1.2° / 0.5° |
In the CDC tables, a positive knee extension value means the knee went past 0° (hyperextension) and a negative value means it stopped short of straight. Knee flexion showed the largest age difference in the study: about 15° between the 2–8 and 45–69 age groups. Knee flexion was measured supine with the hip flexing too, ending when calf met thigh. [3]
AAOS and VA numbers are single reference values, not averages. A dash means we could not verify a value from a source we could check, so we left it out.
Healthy volunteers aged 2 to 69 (674 people) were measured passively by trained physical therapists with a universal goniometer to the nearest degree. Values are mean ± standard deviation, the 95% confidence interval of the mean, and group size.
| Age (years) | Females: mean ± SD (95% CI) [n] | Males: mean ± SD (95% CI) [n] |
|---|---|---|
| 2–8 | 152.6° ± 4.5 (151.2–154.0) [39] | 147.8° ± 4.7 (146.6–149.0) [55] |
| 9–19 | 142.3° ± 5.7 (140.8–143.8) [56] | 142.2° ± 6.3 (140.4–144.0) [48] |
| 20–44 | 141.9° ± 6.3 (140.9–142.9) [143] | 137.7° ± 6.5 (136.5–138.9) [114] |
| 45–69 | 137.8° ± 7.4 (136.5–139.1) [123] | 132.9° ± 6.3 (131.6–134.2) [96] |
Passive ROM, universal goniometer, both sides averaged. Source: CDC[1]; SD and group size from Soucie et al.[2]
| Age (years) | Females: mean ± SD (95% CI) [n] | Males: mean ± SD (95% CI) [n] |
|---|---|---|
| 2–8 | 5.4° ± 4.9 (3.9–6.9) [39] | 1.6° ± 2.5 (0.9–2.3) [55] |
| 9–19 | 2.4° ± 3.5 (1.5–3.3) [56] | 1.8° ± 3.2 (0.9–2.7) [48] |
| 20–44 | 1.6° ± 2.8 (1.1–2.1) [143] | 1.0° ± 2.3 (0.6–1.4) [114] |
| 45–69 | 1.2° ± 2.9 (0.7–1.7) [123] | 0.5° ± 1.9 (0.1–0.9) [96] |
Passive ROM, universal goniometer, both sides averaged. Source: CDC[1]; SD and group size from Soucie et al.[2]
Our clinicians’ step-by-step method for each motion. Use the same position, landmarks and instrument every time you retest.
How we grade sources. A = population study of healthy people with published methods (CDC). B = widely used consensus reference values, as reported in a textbook or peer-reviewed paper; these are single “normal” numbers, not measured averages. C = U.S. government rating standard written for disability evaluation, not as clinical norms. D = expert clinical opinion.
Reviewed by Dr. Richard Holsman, PT, DPT, NCS (Board-Certified Clinical Specialist in Neurologic Physical Therapy), founder of Holsman Physical Therapy. Last reviewed: November 13, 2026.
We re-check every number on this page against its source at least once a year, and sooner if a source is updated or a reader reports a problem. Changes are listed in the change log with the date. To report an error, contact us.
Source: CDC. The CDC normative values are a U.S. government work in the public domain (CDC Stacks marks the study’s data documents “Public Domain”), used under CDC’s Use of Agency Materials terms. The values are shown as published, and the original material is available on CDC’s website at no charge. Our use of CDC material and links to CDC do not imply endorsement by CDC, HHS or the U.S. Government. The VA values come from a federal regulation (38 CFR), also public domain. AAOS values are cited as individual numbers with credit to the publication that reports them; no table layout or text is copied. The goniometry guide is original text by Holsman Physical Therapy.
This page is published by Holsman Physical Therapy and Wellness, P.C., which runs outpatient and in-home therapy practices; that is our only commercial interest. The page carries no advertising, no sponsorship and no affiliate links, and we received no payment from any source for it. We do not sell goniometers or apps. Holsman Physical Therapy is not affiliated with the CDC, the VA, the AAOS, or the authors and publishers cited, and they do not endorse this website.
For clinician education. Norms vary; interpret with clinical judgment. Range of motion differs with age, sex, body type, activity, measurement position, instrument, and whether motion is active or passive. A value outside a reference range is not a diagnosis. Compare with the uninvolved side, retest with the same method, and read the number alongside the patient’s symptoms and function.
Common reference values are 135 degrees (AAOS, as reported by Botman and colleagues) and 140 degrees (VA rating schedule). In the CDC study, healthy adults aged 20 to 44 averaged about 142 degrees (women) and 138 degrees (men) of passive flexion, and 138 and 133 degrees at ages 45 to 69.
Often, yes. In the CDC study the median knee extension for adults was 0 to 1 degree past straight, and some healthy people had 10 degrees or more. Compare with the other knee.
Holsman physical therapists see patients at clinics across North Jersey, the Bronx and Brooklyn, plus in-home visits.
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