The pyramid inch is a unit of measure claimed by pyramidologists

Pyramidology

Pyramidology is a term used, sometimes disparagingly, to refer to various pseudoscientific speculations regarding pyramids, most often the Giza Necropolis and the Great Pyramid of Giza in Egypt...

 to have been used in ancient times. Supposedly it was one twenty-fifth of a "sacred cubit"

Cubit

The cubit is a traditional unit of length, based on the length of the forearm. Cubits of various lengths were employed in many parts of the world in Antiquity, in the Middle Ages and into Early Modern Times....

, 1.00106 imperial inch

Inch

An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot...

es, or 2.5426924 centimetre

Centimetre

A centimetre is a unit of length in the metric system, equal to one hundredth of a metre, which is the SI base unit of length. Centi is the SI prefix for a factor of . Hence a centimetre can be written as or — meaning or respectively...

s.
The first suggestion that the builders of the Great Pyramid of Giza

Great Pyramid of Giza

The Great Pyramid of Giza is the oldest and largest of the three pyramids in the Giza Necropolis bordering what is now El Giza, Egypt. It is the oldest of the Seven Wonders of the Ancient World, and the only one to remain largely intact...

 used units of measure related to modern measures is attributed to Oxford astronomy professor John Greaves

John Greaves

John Greaves was an English mathematician, astronomer and antiquary.-Life:He was born in Colemore, near Alresford, Hampshire. He was the eldest son of John Greaves, rector of Colemore, and Sarah Greaves...

 (1602–1652), who journeyed to Egypt in 1638 to make measurements of the pyramid.