Just the right size for a spare tube, tire levers, patch kit, multi-tool, and house keys. I was looking for a compact and elegant seat back for my fancy new road bike-- this bag is perfect. I wasn't too impressed with the "UPS Sure Post" delivery-- meaning the United States Post Office actually brings it to your house. In my case they left it at the front gate... where it was promptly stolen. Great customer service, though-- Timbuk2 sent a replacement out immediately.