The magnetostatic fields inside and outside of a ferromagnetic thin film, called demagnetizing and stray fields, respectively, are known to be calculable from the model of a uniformly magnetized flat ellipsoid. In this paper, these fields are plotted as functions of the spatial coordinates with the aspect ratios b/a and c/a as parameters. The information is applied to a number of magnetic thin-film device and physics problems. Demagnetizing fields influence wall motion threshold, shape anisotropy, and the stability of domain configuration. Stray fields affect the creeping and switching thresholds of memory elements in an array. The effectiveness of demagnetizing field reduction in a film pair dictates the drive line configuration. In films coupled magnetostatically or by exchange force, the planar components of stray field are important in determining both the quasistatic and dynamic magnetization reversals. However, the normal component of stray field, being much smaller than the normal component of demagnetizing field, has no significant effect on switching.