Surya Siddhanta
योजनानि शतान्य् अष्टौ भूकर्णो द्विगुणानि तु। तद्वर्गतो दशगुणात् पदम् भूपरिधिर् भवेत् ॥
The diameter of the Earth is 1600 Yojanas. Multiply the square of the diameter by 10, the square-root of the product will be the circumference of the Earth.
english translation
yojanAni zatAny aSTau bhUkarNo dviguNAni tu। tadvargato dazaguNAt padam bhUparidhir bhavet ॥
hk transliteration by Sanscript