I don't want my bags checked because i know how horrible greyhound is with luggage. I have a medium sized suitcase, i think it is too big but everyone else says that it is just right. I measured it, and the width is 21 inches, the height is about 14 or 15 inches, and the depth is 4 to 5 inches. Is it too big?
The site didn't tell me anything, so that's obviously why i came here.
And, I can't go try it out. I expect someone to know this from personal experience =)

Greyhound does not give measurements, but says it must be 25 pounds or less and fit under the seat or in the overhead bin. I wish they also gave measurements. Might be a good idea to go try it out before your trip.