The Agni Purana mentions most of the Purana lengths, in terms of the number of shlokas (couplets) that each has.The Brahma Purana - twenty-five thousand
The Padma Purana - twelve thousand
The Vishnu Purana - thirteen thousand
The Vayu Purana - fourteen thousand
TThe Bhagavata Purana - eighteen thousand
The Narada Purana - twenty-five thousand
The Markandeya Purana - nine thousand
The Agni Purana - twelve thousand
The Brahmavaivarta Purana - eighteen thousand
The Linga Purana - eleven thousand
The Varaha Purana - fourteen thousand
The Skanda Purana - eighty-four thousand
The Vamana Purana - ten thousand
The Kurma Purana - eight thousand
The Matsya Purana - thirteen thousand
The Garuda Purana - eight thousand
The Brahmanda Purana - twelve thousand
The only mahapurana which is missing from the above list is the Bhavishya Purana.