Internal overhead in Informix?

I would like (need) to know how much disk space is really needed for an Informix data base. This concerns ordinary tables as well as indices. The manual tells me Informix keeps 9 internal tables, and from the structure I can calculate that for each table there is an administrative record of about 180 bytes, for each field, about 30 bytes, and for each index, about 50 bytes. But it does not say (to me) if any extra space (besides the data) is needed for the records. It also tells me indices are stored as B-trees, so I suppose that for each row in the table the index has to store a pointer, or even two. But I don't know what such pointers look like, and how much space they need. Can anybody point me to more precise information? Many thanks, Reinhard Foessmeier -- <refo@ixos.de> Reinhard Foessmeier | "UNOX estas registrita marko de iXOS GmbH, Bretonischer Ring 12 | Deutsche Lebensmittelwerke GmbH" D-W-8011 Grasbrunn (Germanujo)