Almost exactly the same as the R20, just a bit smaller. And…though comfortable and suitable for all riders, it’s perfect for those under 5.5'. 915 cubic inches of space reside in the main compartment, featuring an internal mesh zipped pocket—all of which is kept secure with a YKK water resistant zip. 3M reflective areas along back and front, and a side access pocket with YKK water-resistant zip makes quick access a snap instead of having to dig through all of your stuff. The internal reservoir pocket with compression straps fits a 3 liter hydration insert (not included). The overall short back length is designed for wearing comfortably along with a hip pack. Add over 300 cubic inches of space by attaching a US-5, or over 600 cubic inches with a US-10. 16.5"×13"×7".