Definition
Density in land use planning refers to the intensity of development on a parcel or area, most commonly expressed as the number of residential dwelling units per acre (du/ac). A single-family home on a 6,000 sq ft lot has a density of about 7 du/ac. A 100-unit apartment building on a one-acre lot has a density of 100 du/ac.
Density is the most fundamental measure of housing intensity, and maximum density limits — typically expressed as a maximum number of units per acre in the zoning ordinance — are the primary regulatory tool cities use to control how much housing can be built in a given area.
Why Density Limits Matter for Housing Policy
Higher density allows more homes to be built on the same land area — which is essential for housing affordability in high-cost California markets where land is scarce and expensive. Lower-density zoning requires more land per dwelling unit, which increases costs per unit and limits housing supply. The vast majority of California's land area in urban communities is zoned for low-density single-family development — a major factor in the state's housing shortage.
Density and RHNA
California's RHNA process assigns each city housing obligations across four income categories: very low, low, moderate, and above moderate. To demonstrate that a site can accommodate lower-income housing, a city's Housing Element must show that the site is zoned at sufficient density — at least 20 du/ac for sites identified for lower-income housing in most of California, and at least 30 du/ac in certain high-cost areas. Sites zoned at lower densities typically cannot be counted toward lower-income RHNA obligations.
Density Bonus Law
California's Density Bonus Law (Government Code § 65915) grants qualifying affordable housing projects the right to exceed the base density set by local zoning. Projects providing a specified percentage of affordable units receive a density bonus ranging from 22.5% (for 10% low-income units) up to 50% (for 24% very low income units), plus waivers from development standards that would prevent achieving the bonus density. Cities must grant this bonus regardless of local zoning limits.
Density limits in residential zoning are the single most important variable in determining how much housing gets built in California. Cities that maintain low-density zoning near transit or in job-rich areas face growing legal pressure — from the builder's remedy, from RHNA obligations, and from state laws mandating higher densities. Legislaide maps the relationship between a city's density limits and its legal obligations under current state law.
Frequently Asked Questions
What is density in land use planning?
Density measures the intensity of residential development on a parcel, typically expressed as dwelling units per acre (du/ac). It is one of the most fundamental zoning metrics — directly controlling how many homes can be built on a piece of land.
How is density measured?
The most common measures are: gross density (units per total land area including roads and open space), net density (units per developable land area excluding public rights-of-way), and floor area ratio (FAR, which measures building area as a multiple of lot area rather than counting units directly).
What are California's minimum density requirements for housing?
Housing Element sites for lower-income RHNA must generally be zoned at a minimum of 20 du/ac (or 30 du/ac in larger urban jurisdictions) to be credited toward the Housing Element allocation. Sites zoned below the required minimum density cannot count for lower-income RHNA categories.
How does density relate to RHNA compliance?
RHNA compliance requires demonstrating that enough land is zoned at sufficient densities to accommodate the allocation across income levels. Sites with inadequate minimum density cannot be credited for lower-income RHNA. This is why density minimums directly affect whether a Housing Element can be certified by HCD.
How does the Density Bonus Law affect local density caps?
The Density Bonus Law entitles qualifying affordable housing projects to exceed local density limits by a specified percentage (up to 50%), plus waivers from development standards that would prevent achieving the bonus. State law effectively overrides local density caps for qualifying projects — agencies cannot deny the additional density.
Published June 1, 2026 by Legal Team at Legislaide.