Knee Brace Sizing Chart: How to Measure the Thigh

General product information only, not medical advice. A clinician decides whether a knee brace is appropriate and which one.

This page is for anyone holding a knee brace size chart and a tape measure who wants to know which number to read off and what it means. The short answer: knee brace sizes are set by each manufacturer, so the chart that came with your brace is the one that counts. The table below is one real example, the X8 knee brace from Cascade (Mobius), copied from the maker’s own sizing sheet.

The chart: X8 knee brace sizes by thigh circumference

This is a single manufacturer’s chart for a single product, not a universal knee brace size chart. Source: Cascade, X8 Knee Brace Sizing sheet (PDF dated 14 April 2025, checked 31 October 2026).

Size	Thigh circumference (inches)	Thigh circumference (cm)
XS	15 to 17	38 to 43
S	17 to 19	43 to 48
M	19 to 21	48 to 53
L	21 to 23	53 to 58
XL	23 to 25	58 to 63

Check your product’s labelling. Use the sizing sheet or packaging for the exact brace you own. Another brand, or another model from the same brand, can use different ranges and a different measuring point.

How to read the chart

Find your measured thigh circumference in the middle or right-hand column and read the size from the left. The ranges meet at their end points (17 inches is both the top of XS and the bottom of S), so a measurement exactly on a boundary is a between-sizes case. For the X8, the maker’s rule is: “If the measurement falls between two sizes, select the smaller size.” That is the X8 rule, not a general one; other makers may tell you to size up or to call them.

How to measure for this chart

The X8 measuring protocol states: “From the center point of the kneecap, measure 6 inches vertically, or up the thigh, then measure the circumference of the thigh at this point.” In practice that means three things: the landmark is the centre of the kneecap, the distance is 6 inches (about 15 cm) straight up the thigh, and the number you record is the distance around the thigh at that spot, not around the knee.

Performance Health’s support article for its Hypercontrol knee brace uses the same landmark: the brace “is sized by measuring the circumference of the thigh, 6″ above the knee of the mid patella.” Two makers agreeing does not make 6 inches a rule for every brace. Some products are sized from a different point or from the knee itself, so read the instructions for yours.

Equivalence notes: inches and centimetres

The X8 sheet prints both units. The conversion is 1 inch = 2.54 cm, and the sheet’s centimetre figures are rounded to whole numbers (17 inches is 43.18 cm, printed as 43). Measure in whichever unit your chart uses rather than converting, so rounding never moves you across a boundary.

Common mix-ups

Treating one brand’s chart as universal

An “M” on one brand’s chart has no fixed meaning on another’s. Generic tables online that list S, M and L ranges without naming a manufacturer or a document cannot be traced to a source, so this page does not reproduce one.

Measuring at the wrong spot

Measuring at the widest part of the thigh, or at the knee, gives a different number than the X8 and Hypercontrol landmark above. Follow the landmark in your product’s own instructions.

Applying the between-sizes rule from another product

The X8 says to take the smaller size. That instruction belongs to that product’s sheet.

Expecting a regulatory size standard

Under 21 CFR 890.3475, a limb orthosis (brace) is a Class I device, exempt from premarket notification (510(k)) subject to the limitations in 21 CFR 890.9. The section defines the device and its classification; it does not set a size chart. Sizing therefore comes from the manufacturer’s labelling.

Frequently asked questions

Is there one standard knee brace size chart?

No chart is set by the federal classification regulation for limb orthoses (21 CFR 890.3475). Each manufacturer publishes its own, as in the X8 example above.

Which measurement do knee brace charts use?

The X8 sheet and the Hypercontrol support article both use thigh circumference 6 inches above the centre of the kneecap. Other products may differ, so follow the sheet for your brace.

What if I am between two sizes?

Follow the rule printed for your product. The X8 sheet says to select the smaller size.

Related guides

Sources

Cascade (Mobius), X8 Knee Brace Sizing sheet, PDF dated 14 April 2025: cdn.cascade-usa.com. Checked 31 October 2026.
Performance Health support, Hypercontrol Knee Brace: support.performancehealth.com. Checked 31 October 2026.
21 CFR 890.3475, Limb orthosis (as amended 4 December 2025): law.cornell.edu. Checked 31 October 2026.

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