Petrie measured the lowest layer to be 148 centimetres (4.86 ft) high, whereas the layers towards the summit barely exceed 50 centimetres (1.6 ft).[93]
The accuracy of the pyramid's perimeter is such that the four sides of the base have an average error of only 58 millimetres (2.3 inches) in length[b] and the finished base was squared to a mean corner error of only 12 seconds of arc.[96]
The completed design dimensions are measured to have originally been 280 royal cubits (146.7 m; 481.4 ft) high by 440 cubits (230.6 m; 756.4 ft) long at each of the four sides of its base. Ancient Egyptians used seked – how much run for one cubit of rise – to describe slopes. For the Great Pyramid a seked of 5+1/2 palms was chosen, a ratio of 14 up to 11 in.[97]
Some Egyptologists suggest this slope was chosen because the ratio of perimeter to height (1760/280 cubits) equals 2π to an accuracy of better than 0.05 percent (corresponding to the well-known approximation of π as 22/7). Verner wrote, "We can conclude that although the ancient Egyptians could not precisely define the value of π, in practice they used it".