Urban Growth Boundary Calculator

Population growth compounds annually rather than adding a flat amount each year, so even a modest difference in Annual Growth Rate -- say 2% versus 3% -- produces a meaningfully different Projected Population after 20 years of compounding, the same way a difference in interest rate compounds into a large gap in an investment balance over time. That's why small, defensible growth-rate assumptions matter more than they might first appear.

Land Capacity is a supply-side figure driven entirely by acreage and density -- Vacant Buildable Land and Redevelopable Land multiplied by Target Density (and the density gain from redevelopment). Avg. Household Size only converts between population figures and housing-unit figures on the demand side, translating Population Growth into Housing Units Needed, so it never changes how many units the land itself can physically hold.

Vacant land starts from zero, so its full Target Density becomes new capacity. Redevelopable land is already built at Current Avg. Density, so redeveloping it only adds the difference between the target and current density -- an acre going from 6 to 10 units per acre gains 4 units of new capacity, not 10, because the existing 6 units per acre were already there.

It means Housing Units Needed over the planning horizon exceeds Land Capacity -- the units the vacant and redevelopable land inside the current boundary could supply at your target density -- so the projected population can't be accommodated without either expanding the boundary, raising the target density further, or slowing growth. Expansion Needed (acres) estimates how much additional land would close that specific gap.