7" width side to side; 13" length from the front bend to the rear (but you can loosen a couple screws to make it longer (dunno how much longer since I haven't extended it); 15" from top to the wheel hub. The issue, though, is the tube diameter is 3/4" which will eliminate many of the panniers that are designed to clip on quickly (such as Bikase grocery pannier which doesn't fit for that reason).