The average weight of the stone blocks used to construct Giza's Great Pyramid has been calculated to be 2.5 tonnes (2.5 tons). The exact number of blocks used in the construction of the pyramid is unknown. The pyramid was never fully excavated, so evidence such as stonework and rubble that may have contained valuable information about the construction process were lost when the area it was found in was developed. In 1877, British archaeologist Charles Newton made an estimation of block weights based on measurements of two sides of the pyramid. He estimated that the heaviest block used in its construction had a mass of about 2.5 tonnes and the lightest one about 0.4 tonnes. More recently, in 1998, American archaeologists conducted an intensive study of the pyramid using ground-penetrating radar. They concluded that each block of limestone used in building the pyramid was equivalent to 7.5 yd3 or 6.5 cu meters of dirt. This implies a total weight for all the blocks of about 60,000 kg (132,000 lb), which is very close to Newton's estimate. However, the actual weight of a single block used in construction of the pyramid has not been determined by this study.