FRS (1 October 1671 – 4 July 1742) was an Italian monk, priest, philosopher, theologian, mathematician, and engineer.

In 1693 he was sent to the Monastery of St. Gregory the Great, the Camaldolese house in Rome, to complete his studies in philosophy and theology in preparation for Holy Orders.

He did his research privately, however, as he was appointed professor of philosophy at St. Gregory Monastery in 1700, subsequently holding a post in the same field in Pisa, where he replaced Pascasio Giannetti.

By 1707, however, Dom Grandi had developed such a reputation in the field of mathematics that he was named court mathematician to the Grand Duke of Tuscany, Cosimo III de Medici.

In that post, he also worked as an engineer, being appointed Superintendent of Water for the Duchy, and in that capacity, he was involved in the drainage of the Chiana Valley.