How tall can a saguaro cactus grow?

The height depends upon the type of cactus. There in fact is quite a range in possible cactus heights. For example, a cactus plant may be tall, such as the 40 foot/12 meter giant saguaro cactus [Carnegiea gigantea]. Or it may be small, such as the 2 inch/5 centimeter Ariocarpus fissuratus, which is one of the living rock or fossil cactus plants.

The tallest cactus is the cardon cactus (Pachycereus pringlei)of Mexico which grows to 63 feet or more in height.

17Wolf359 added: There are actually number of cactus taller and bigger that both C. gigantea and P. pringlei. The tallest reported cactus at over 80 feet is Pachycereus grandis. Pachycereus weberi, Backebergia militaris, Neobuxbaumia macrocephala, Trichcereus tersheckii and Neocardensia hertzogonia are all of similar size or larger than C. gigantea or P. pringlei.