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Residential Density Calculator: Units per Acre, Maximum Units and Gross vs Net

Work out the maximum dwelling units a parcel allows under a zoning density cap (units per acre or per hectare) or a minimum lot size, on gross or net area, with rounding rules and a density bonus. Convert between du/ac and du/ha, compare gross and net density after streets and open space, and estimate land per unit, population and parking.

Parcel area

Zoning maximum density

Density cap applies to

Minimum lot size (0 if density-based)

Land lost to streets, stormwater, open space

Proposed units (0 to size to the max)

Fractional units

Density bonus

Persons per household

Parking spaces per unit

Surface parking area per space (incl. aisles)

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How it works

Gross density = units ÷ total acres · net density = units ÷ (acres × (1 − infrastructure %)) · max units = min(round(cap area × du/ac × (1 + bonus)), ⌊net ft² ÷ minimum lot⌋) · 1 du/ac = 2.471 du/ha · land per unit = net area ÷ units

Residential density is counted in dwelling units per acre (du/ac) or per hectare (du/ha), but the number means little until you know whether it is gross or net. Gross density is measured over the whole parcel, including future streets and parks; net density is measured over the lots themselves. The gap is typically 20–30% on a new subdivision, and ordinances say which one they regulate, so choose the basis your code uses. Zoning may cap density directly, through a minimum lot size, or both, and the more restrictive rule governs. Most codes round fractional units down, but some round to the nearest unit, and state density bonus laws (such as California’s) round up. Bonuses for affordable housing add a percentage to the base density. The calculator gives the maximum unit count, or checks a proposed count against it. It converts between du/ac and du/ha and shows the land per unit, population at your household size and parking demand (surface parking at suburban ratios can take a fifth of the site). The yield table shows how many units other density caps would allow. Density also decides whether a neighbourhood can support frequent transit and local shops; studies generally place that threshold somewhere above 7–15 units per acre.

Worked example

A 10-acre parcel zoned 12 du/ac (gross) allows 10 × 12 = 120 units. With 25% of the land in streets and open space the net area is 7.5 acres, so those 120 units are 12 du/ac gross (29.7 du/ha) but 16 du/ac net (39.5 du/ha), townhouse density, with 2,723 ft² (253 m²) of net land per unit. At 2.5 persons per household that is 300 residents, and at 1.5 spaces per unit, 180 parking spaces covering about 1.3 acres of surface lot. If the code measured density on net area instead, the cap would allow 7.5 × 12 = 90 units.

Sources: U.S. Census Bureau QuickFacts — persons per household, 2020–2024 · Urban density — Wikipedia (gross vs net density)

Frequently asked questions

How many units per acre is a typical suburb?

Large-lot suburbs run 1–3 du/ac, standard post-war subdivisions 4–6, small-lot and duplex neighbourhoods 8–12, townhouses 12–20, garden apartments 20–35 and mid-rise buildings 50–100 or more.

What is the difference between gross and net density?

Gross density divides the units by the whole parcel; net density divides them by the land left for lots after streets, stormwater ponds and open space. The same 120 units on 10 acres are 12 du/ac gross but 16 du/ac net when a quarter of the land goes to infrastructure.

How do I convert units per acre to units per hectare?

Multiply by 2.471 (one hectare is 2.471 acres): 12 du/ac = 29.7 du/ha. To go back, divide by 2.471 or multiply by 0.4047.

Do I round fractional units up or down?

Most codes round down, so 10.6 allowed units means 10. Some round to the nearest whole unit, and state density bonus laws such as California’s require rounding up. Choose the rule under More options.

Do accessory dwelling units count?

Increasingly no. Many states and cities exempt ADUs from density limits to encourage them, so check the ADU provisions separately from the base density.

Related calculators

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Calculate floor area ratio (FAR, also called FSI or plot ratio) from lot size and gross floor area, or the maximum buildable floor area under a zoning FAR limit with bonuses. See the storeys and building height that area needs at a given lot coverage, whether a height limit binds before FAR, excluded areas, net rentable area and the number of units it could hold.

Setback, Lot Coverage & Buildable Area Calculator

Find the buildable envelope of a rectangular lot after front, rear and side setbacks, the maximum footprint under a lot coverage limit, impervious surface limits with driveway and patio, the largest house that fits, and whether a proposed footprint complies.

Parking Requirement Calculator (Spaces by Use)

Calculate the minimum parking spaces a zoning code requires from floor area, dwellings, rooms or seats for each use — office, retail, restaurant, medical, warehouse, residential, hotel, assembly, school — for up to three mixed uses with a shared-parking (time-of-day) credit, reductions, rounding, accessible (ADA), EV and bicycle spaces, a check of the spaces you provide, and the land and cost the parking takes.

Population Density Calculator

Work out population density from a head count and an area in any common unit, and see the equivalent density per square kilometre and per square mile.

Planning arithmetic using the definitions most zoning codes share; the actual FAR, setbacks, height, coverage, parking ratios and density rules are set by the local ordinance and overlay districts, and many cities exclude or bonus certain areas. Confirm with the zoning code and a land-use professional before relying on a yield.