Modern urban housing densities, actual or proposed, show enormous variation. 'Broadacre City', Frank Lloyd Wright's proposal from the early 1930s, for example, was several thousand times less dense than the Liverpool docks had been in the middle of the previous century. What housing densities should we aim for? The determinants of housing densities can be thought of as either internal or external to habitation. The former concern the space households acquire or are allocated to satisfy the functions or desires of habitation; the latter are those forces, external to habitation, which influence density, such as the provision of public transport, the profit seeking behavior of developers or government policy to slow urban spread. I begin with some brief reminders of how in the recent past when urban compaction theory or practice has been in the ascendancy (internal) considerations of habitation have not been given due weight. Is this the case again? I compare a sample of higher density housing types and schemes in Brisbane with Copenhagen, a denser city admired by compact city advocates. This comparison produces some surprising results about relative densities and should give us cause to think again about levels of amenity and the usefulness of external space in our higher density housing, whatever our beliefs about the need for such densities.