Square feet is the unit of construction: floor plans, builder quotes, and per-square-foot land prices all use it. Land records in eastern India and Nepal, however, are written in bigha. Converting between the two is a single multiplication once you know the size of your local bigha — and that is the catch, because the bigha is not one unit but a family of regional units.
The figures on this page follow our converter: the Assam/West Bengal bigha of 14,400 sq ft, which is exactly 1,600 gaj (a gaj being one square yard, 9 sq ft), and the Nepal Terai bigha of 72,900 sq ft. The gaj relationship is worth remembering — many north Indian property dealers quote plots in gaj, and "1 bigha = 1,600 gaj" converts mentally far more easily than the square-feet figure.