Estimate Units Allowed From Density Rules

Residential density is the number of dwelling units per acre of land, expressed as units per acre (DU/acre). It's calculated by dividing the total number of dwelling units by the site area in acres: Density = Number of Dwelling Units ÷ Site Area (acres). For example, 20 units on a 2-acre site equals a density of 10 units per acre (20 ÷ 2 = 10). This metric is fundamental to zoning regulations and helps communities manage growth, infrastructure capacity, and neighborhood character. Density applies to all housing types including single-family homes, townhomes, apartments, and accessory dwelling units (ADUs).

Gross density uses the total site area including all land within the parcel boundaries, such as roads, open space, wetlands, and other non-buildable areas. This provides an overall sense of how densely an area is developed. Net density uses only the developable portions of the site, excluding constrained areas like public rights-of-way, critical areas (wetlands, floodplains, steep slopes), dedicated open space, and other areas where building is prohibited or restricted. The same number of units will always result in a higher net density than gross density because net excludes non-buildable areas. Your local zoning code will specify which calculation method applies to your district, so check your zoning ordinance to see whether it wants gross or net area. The gap is not small. A parcel with a 30% right-of-way dedication can pass on net density and fail on gross, or the reverse, depending on which number the code puts the cap against.

No, this calculator does not look up or interpret zoning codes. It simply performs the mathematical calculation of units divided by acres and compares your result to any maximum or minimum density values you enter manually. You must research your local zoning ordinance separately and enter those values manually for comparison. Zoning codes are specific to each jurisdiction and can be found on your city or county's planning department website. This tool is designed for planning purposes only and does not provide professional zoning interpretation or final development capacity determinations. Always consult your local planning department for official zoning information and compliance verification.

Check your local zoning ordinance, which is usually available on your city or county's planning department website. Look for your property's zoning district designation (e.g., R-1, R-2, R-3, MF-1, MF-2), then find the dimensional standards or development standards section for that district. The density limits will be listed as maximum and/or minimum units per acre. You can also contact your local planning department directly for assistance, or use online zoning map tools if your jurisdiction provides them. Some jurisdictions have interactive zoning maps that show your property's zoning district when you enter an address.

Units per acre applies to all housing types but translates differently depending on the product. For single-family homes, it typically translates to lot sizes (e.g., 4 units/acre = roughly 10,000 sq ft lots, meaning each lot is about 0.25 acres). For townhomes, 10–15 units/acre is common, with each unit typically occupying 2,000–5,000 sq ft including shared walls and common areas. For apartments, density can range from 20–60+ units/acre depending on building height, with garden apartments (2–3 stories) at 15–25 units/acre and high-rise apartments (7+ stories) at 60–200+ units/acre. The same density can look very different depending on the housing product. Higher density doesn't necessarily mean taller buildings, since townhomes can reach moderate density through efficient site design. The same density number on paper can produce very different neighborhoods on the ground.

Minimum density requirements encourage efficient land use, particularly near transit, employment centers, and urban cores. They help support public transit ridership by ensuring adequate population density to make transit viable, maximize housing production in high-demand areas where land is scarce and expensive, ensure adequate population to support neighborhood retail and services, and prevent land speculation that holds parcels for future higher-value uses instead of current development. Minimum density requirements are increasingly common in urban areas and transit-oriented development zones as cities seek to address housing shortages and promote sustainable development patterns.

Not always. While you may be allowed a certain density by the zoning code, other regulations often further limit actual development capacity. Setbacks (required distances from property lines) may reduce buildable area, height limits may cap the number of stories you can build, parking requirements may consume significant land area, open space minimums may require dedicating land for landscaping or recreation, lot coverage limits may restrict how much of the site can be covered by buildings, floor area ratio (FAR) limits may cap total building square footage, and environmental constraints (wetlands, floodplains, steep slopes) may reduce developable area. This calculator only addresses density. A full development analysis has to run every one of those standards, and one of them usually bites before the density cap does. Density sets the ceiling on paper; site design lowers the real unit count.

Many jurisdictions offer density bonuses that allow developers to exceed base zoning limits in exchange for providing public benefits like affordable housing, public amenities, or green building features. For example, including 15% affordable units might grant a 35% density bonus, allowing you to build 35% more units than the base maximum. Bonus programs vary by jurisdiction and may require specific percentages of affordable housing, public open space, transit improvements, or other community benefits. The bonus is typically calculated as a percentage increase over the base maximum density. Check with your local planning department about available bonus programs, eligibility requirements, and application procedures. If a bonus program applies, read the fine print before you assume the extra units are actually available.

Use the total number of dwelling units, including affordable units, accessory dwelling units (ADUs), and any other residential units. Density calculations typically count all dwelling units regardless of price point or unit type. However, some bonus density programs may calculate certain unit types differently (e.g., affordable units may count differently for bonus calculations), so check your local regulations. The general rule is to count all residential units that will be built on the site, including market-rate apartments, affordable units, townhomes, single-family lots, and ADUs. For bonus programs or special overlays, confirm the counting rules before you lock in a yield.

You can enter your site area in square feet, and the calculator will convert it to acres automatically using the standard conversion factor of 43,560 square feet per acre. For example, 108,900 square feet ÷ 43,560 = 2.5 acres. If you enter both acres and square feet, the acres value will be used. You can verify the conversion in the results to ensure accuracy. This conversion is essential because density is always expressed in units per acre, regardless of how you measure your site area. A simple unit mistake here can throw off the entire feasibility check.

They're a rough ladder from least to most dense residential, but the actual numbers are local, so treat these as typical rather than fixed. R-1 is usually single-family detached on larger lots, often around 1 to 6 units per acre. R-2 tends to allow single-family plus duplexes, roughly 6 to 12 units per acre. R-3 opens up to townhomes and low-rise multifamily, commonly 12 to 30 or more. A number of cities run the scale the other way (R-1 as the densest), and plenty use letters like RS, RM, or RH instead. The only figure that governs your parcel is the one printed in your own zoning ordinance for that district. Look it up, then enter the max and min here to check your unit count against it.

You can use the optional scenario label field to name different concepts (e.g., 'Townhome Option A', 'Apartment Concept B'), then use the download feature to save a text report for each scenario. This allows you to compare different unit counts, layouts, or housing mixes for the same site. Each scenario will show its own density calculation and comparison to your entered limits. Comparing scenarios helps you evaluate different development options and understand how unit count, site area, and density limits interact. That is useful when you are comparing yield before paying for a full entitlement study.