|MadSci Network: Cell Biology|
The average dimensions of mammalian cells range from about 10 to 50 microns. Isolated muscle cells are on the large side and neurons without their dendritic arbors are smaller, other cell lines will fall in between. Make sure your well surface is conducive to the cells sticking (it may need to be coated or specially treated). Dmitri See Molecular Biology of the Cell by Bruce Alberts for more info.
Try the links in the MadSci Library for more information on Cell Biology.