Āryabhaṭa calculated the Earth's circumference and landed within a few percent of the true value.
The Āryabhaṭīya gives Earth's diameter as 1,050 yojanas; with the period's yojana this yields a circumference of ~39,968 km.
— Āryabhaṭa, Āryabhaṭīya (499 CE)
Earth's actual circumference: ~40,075 km.
A genuine, defensible parallel.
Āryabhaṭa's figure works out astonishingly close to the modern value — within about 1% — a remarkable result for the 5th century, achieved through geometry and observation rather than direct measurement of the whole globe. It sits alongside his rotating-Earth model and correct shadow theory of eclipses as part of a genuinely advanced mathematical astronomy.
The honest caveat is the usual yojana problem: the exact match depends on which value of the yojana you assume, and estimates vary, so '1%' is a best-case reading. Eratosthenes in Greece had also estimated Earth's size centuries earlier. Still, Āryabhaṭa's astronomy was rigorous and his figure is genuinely in the right ballpark.