This paper addresses two issues in the subjective measurement of density, (a) whether perceived density is influenced by the sizes and spacing of buildings and (b) whether perceived density is influenced by surface details. Two experiments were conducted. Stimuli in Exp. 1 were 9 photomontages of rows of residential buildings. Factors were (a) building surface area (at low, medium, and high levels) and (b) layout (many small buildings and small gaps to few large buildings and large gaps, in three levels). Amount of visible building surface area accounted for 63% of variance of scaled impressions of density, while layout accounted for 15% of variance. Stimuli in Exp. 2 were grey boxes with the same factors of building surface area and layout. Scaled impressions of density of buildings and boxes correlated at .95, suggesting that surface detail had a minor effect in perceived density.