Good question! I love reading others' responses. I have 4 kids, and the oldest two boys are 14 and 12. We have daily morning chores (feed the dog, empty the dishwasher, take out the garbage, make their beds and clean up dirty laundry). In the evening, the kids must fold any clothes that have been washed and put them away. They help with dinner, including clean-up.
The days are extremely busy, so we feel satisfied that these basic chores are enough. Overall, it should take them no more than 20-30 minutes to complete everything - usually divided between morning and night. On the weekends, to earn video-game time, we require additional chores including yard work, vacuuming, cleaning their bathrooms, emptying wastebaskets, and more. We'll also send them to the grocery store across the street occasionally.