— The Aryabhatiya of Aryabhata, tr. W. E. Clark (1930)ch1.v5
In short: Aryabhata (499 CE) gives the diameter of the Earth as 1,050 yojanas (~13,200 km using ~12.5 km/yojana), within ~3% of the modern value of 12,742 km — a striking pre-modern measurement.
Multiple sourcesv2The Aryabhatiya of Aryabhata, tr. W. E. Clark (1930), ch1.v5