I mainly use this pack for day hikes.  I'm 5'2" tall and ordered the sand gold color in size small/medium.  I bought this pack because I wanted something small, lightweight, and with a well designed hydration system.  This Raptor 18 is perfect for my needs!!  On a typical day hike, the Raptor 18 is big enough to carry my rain jacket & rain pants, down jacket, knitted hat, gloves, bandana, small first aid kit, cell phone, wallet, keys, and snacks.  A big plus about this pack is I don't feel the water bag bulging into the middle of my back when it's filled to the max (3 liters).  I also use the Raptor 18 for what it's designed for...bike rides.  On longer road bike rides, when I need to carry warmer bike clothing, rain gear, more water, and more snacks, the Raptor 18 is the best in size and comfort!!!!