The exact quantity depends on your floor plan, the number of light and socket points and the wiring layout, but the following gives a sound planning estimate. House wire is sold in 90-metre coils, and you generally use three sizes: 1.5 sq mm for lighting, 2.5 sq mm for general sockets, and 4 sq mm for heavy appliances such as ACs and geysers.
For a typical 2 BHK, budget around 3 coils each of 1.5 and 2.5 sq mm, plus one or two coils of 4 sq mm. For a 3 BHK, allow roughly 4–5 coils each of the lighting and socket sizes and about two coils of 4 sq mm. Add a heavier size (6 sq mm or more) for the incoming mains run.
Always add a margin for wastage, offcuts and future points — running short mid-job is far costlier than a spare coil. For an accurate bill of quantities, let your electrician count the actual points and runs from the wiring diagram. Our home-wire estimator breaks this down by size.