The Great Pyramid of Giza (also called the Pyramid of Khufu and Pyramid of Cheops) is the oldest and largest of the three pyramids in the Giza Necropolis bordering what is now Cairo, Egypt, and is the only one of the Seven Wonders of the Ancient World that survives substantially intact. It is believed the pyramid was built as a tomb for Fourth dynasty Egyptian King Khufu (Cheops in Greek) and constructed over a 20 year period concluding around 2560 BC. The Great Pyramid was the tallest man-made structure in the world for over 3,800 years.

Originally the Great Pyramid was covered by casing stones that formed a smooth outer surface, and what is seen today is the underlying core structure. Some of the casing stones that once covered the structure can still be seen around the base. There have been varying scientific and alternative theories regarding the Great Pyramid's construction techniques.

Most accepted construction theories are based on the idea that it was built by moving huge stones from a quarry and dragging and lifting them into place. There are three known chambers inside the Great Pyramid. The lowest chamber is cut into the bedrock upon which the pyramid was built and was unfinished.

The so-called Queen's Chamber and King's Chamber are higher up within the pyramid structure. The Great Pyramid of Giza is the main part of a complex setting of buildings that included two mortuary temples in honor of Khufu (one close to the pyramid and one near the Nile), three smaller pyramids for Khufu's wives, an even smaller "satellite" pyramid, a raised causeway connecting the two temples, and small mastaba tombs surrounding the pyramid for nobles. It is believed the pyramid was built as a tomb for Fourth dynasty Egyptian pharaoh Khufu and constructed over a 14 to 20 year period concluding around 2560 BC.

Khufu's vizier, Hemon, or Hemiunu, is believed by some to be the architect of the Great Pyramid. It is thought that, at construction, the Great Pyramid was originally 280 Egyptian cubits tall, 146.6 meters, (480.97 feet, or about 40 stories) but with erosion and the loss of its pyramidion, its current height is 138.8 m (455 feet). Each base side was 440 royal cubits, 230.5 meters in length, (756.2 feet).

A royal cubit measures 0.524 meters. The total mass of the pyramid is estimated at 5.9 million tonnes. The volume, including an internal hillock, is believed to be roughly 2,500,000 cubic meters.

Based on these estimates, building this in 20 years would involve installing approximately 800 tonnes of stone every day. The first precision measurements of the pyramid were done by Egyptologist Sir Flinders Petrie in 1880–82 and published as The Pyramids and Temples of Gizeh. Almost all reports are based on his measurements.

Many of the casing stones and interior chamber blocks of the great pyramid were fit together with extremely high precision. Based on measurements taken on the north eastern casing stones, the mean opening of the joints are only 0.5 millimeters wide (1/50th of an inch). The pyramid remained the tallest man-made structure in the world for over 3,800 years, unsurpassed until the 160 meter tall spire of Lincoln Cathedral was completed c.

1300. The accuracy of the pyramid's workmanship is such that the four sides of the base have a mean error of only 58 millimeter in length The base is horizontal and flat to within 15 mm. The sides of the square base are closely aligned to the four cardinal compass points (within 4 minutes of arc) based on true north, not magnetic north, and the finished base was squared to a mean corner error of only 12 seconds of arc.

The completed design dimensions, as suggested by Petrie's survey and later studies, are estimated to have originally been 280 cubits in height by 440 cubits in length at each of the four sides of its base. These proportions equate to π/2 to an accuracy of better than 0.05% (corresponding to the approximation of π as 22/7). Some Egyptologists consider this to have been the result of deliberate design proportion.

Verner wrote, "We can conclude that although the ancient Egyptians could not precisely define the value of π, in practise they used it". Petrie, author of ‘The Pyramids and Temples of Gizeh', who was the first accurate surveyor of Giza and the excavator and surveyor of the Pyramid of Meidum, concluded: "but these relations of areas and of circular ratio are so systematic that we should grant that they were in the builders design". Earlier in the chapter he wrote more specifically, that: “We conclude therefore that the approximation of 7 to 22 as the ratio of diameter to circumference was recognised”.

These proportions equated to the four outer faces sloping by approximately 51.842º or 51º 50' 35", which would have been understood and expressed by the Ancient Egyptians as a seked slope of 5 1/2 palms .

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