Two distant mountain bikers riding along a mountain towards the setting sun.

All Trek mountain bikes use alpha sizing instead of numeric sizing. Rather than labeling our bikes with size numbers like 17.5 and 19.5, we use sizes like M (medium) and L (large).

Why alpha sizing?

1. It’s easier to understand
“Medium” is intuitive. “17.5” is not. Alpha sizing makes it easier for you to know what Trek mountain bike will work for you. A lot of other brands also use alpha sizing, and if you ride a medium in a different brand, you’ll probably ride a medium Trek as well.
2. Frame sizes are measured differently today
Trek frame size used to be measured by the length of the seat tube. But modern mountain bike geometry is based on reach, not seat tube length. Alpha sizing is simpler and helps you find the right fit by the measurement that matters most.

Sizing conversion

The new alpha sizing corresponds with the previous numeric sizing for all models:

Alpha size XS S M ML L XL XXL
Frame size 13.5 15.5 17.5 18.5 19.5 21.5 23
Rider height 147-155 cm
4’9”-5’1”
153-162 cm
5’2”-5’3.8
161-172 cm
5’3.4”-5’7.7”
170-179 cm
5’6.9”-5’10.5”
177-188 cm
5’9.7”-6’2”
186-196 cm
6’1.2”-6’5.2”
195-203 cm
6’4”-6’7.9”

Extended size range

Trek offers mountain bikes in a wide range of sizes to ensure the perfect fit for all riders. That includes an XS with increased standover height, an ML (medium-large) perfect for those in-betweeners in the middle of the sizing bell curve, and an XXL for taller riders who often struggle to find a bike that’s big enough.

Not all sizes are available on all models, but Trek’s extended size range will help any rider find a frame that fits better from the start and requires fewer changes to the cockpit.

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