Now the volumes of the inside of the G2 coffer 84.73 x 26.69 x 29.59 = 66,816.11908 cubic inches x 3.125 = 209,112.8721 cubic inches equals the outside volume including the height of the lid 208,956.6098 cubic inches.
When you look you can see what they have done the outside volume = 120.96 cubic feet / 3.125 = 38.7072 cubic feet for the inside. 66,886.0416 cubic inches.
And the inside volume and this is all in imperial feet is most probably 1/2,020,000th the volume of the pyramid itself = 78,188,544 cubic feet.
You can check this with Petrie's figures he is working in inches so we will do the same 135109804 / hgt 5664 = 23,854,132.07 cubic inches x 3 = 71,562,396.2 cubic inches square root = 8459.456 inches. The actual height is the problem and Petrie gave 13 inches margin of error. But never the less pretty darn close to his mean for base of 8474.9.
They are using imperial feet.