A quasi-two-dimensional model is developed to calculate domain structures in magnetite grains containing two to 20 domains. The calculation shows that ''domains'' do not consist of uniformly magnetized regions, consistent with the conclusions previously carried out on sub-micron grains, but that they become more uniformly magnetized for grains containing several domains, consistent with domain imaging results. In spite of improvement over previous calculations, there remains a significant difference between the number of domains observed and calculated. ¿ American Geophysical Union 1991