An average horse has a 3,6 meter stride which approximately corresponds to 12 feet, or 4 human steps. For ponies this distance is reduced to an average of 3 meters or 9ft 9 in. Keep in mind that this distance is only an indication and can vary from one horse/pony to another.
When measuring the distance between two jumps the convention is to allow 6 feet for the landing of the first jump and 6 feet for the take off of the second one.