Zoning calculator
Units Per Acre Calculator (Residential Density)
Work out how many dwelling units a site allows under a units-per-acre cap or a minimum lot area per unit, or the density of a planned project, using gross or net acreage.
Units per acre calculator
Example figures are filled in. Replace them with your own.
Gross site area, best from a survey or recorded plat. Assessor figures are often rounded.
If the code counts net acreage, e.g. street right-of-way. Check your code.
Units the density allows
57
3.2 site acres (139,392 sq ft) at 18 units per acre
3.2 acres × 18 = 57.6, rounded down to 57
Rounded down. Some codes round differently, cap units per lot, or grant bonuses (including under state law), and parking, height, and FAR limits can allow fewer units.
Arithmetic only, on the numbers you enter. Zoning rules and definitions differ by municipality, so confirm them in the local code or with the planning department before relying on a result.
Residential density is the number of dwelling units on a site divided by its area in acres. One acre is 43,560 square feet, so a 2-acre site with 36 units has a density of 18 units per acre. Codes cap density in different ways, and the calculator handles the two most common.
How to use the calculator
- Enter the site area in acres or square feet.
- If your code measures density on net acreage, enter the area it leaves out, such as street right-of-way.
- Choose a units-per-acre cap, a minimum lot area per unit, or the density of a project, and enter the figure.
How codes set density
- Units per acre. Miami caps density by Transect Zone: 36 units per acre in T4, 65 in T5, and 150 in the T6 zones.
- Minimum lot area per unit. Austin's multifamily districts require a minimum site area for each unit, varying by unit size. In MF-2 it is 1,600 square feet for an efficiency, 2,000 for a one-bedroom, and 2,400 for two or more bedrooms. At 2,400 square feet per unit, that works out to about 18 units per acre. When a code varies the figure by unit type, run each type separately.
- Floor area per unit. New York City divides the maximum residential floor area by a dwelling unit factor, generally 680, to get the maximum number of units.
- Units per lot. Some districts cap units per lot regardless of size. Austin's SF-3 district allows up to three.
What changes the answer
- Gross or net area. Detroit leaves public rights-of-way out of lot area. Miami also uses lot area without rights-of-way, but lets rights-of-way dedicated since the last recorded plat count toward density. Use the area your code specifies.
- Rounding. The calculator rounds fractional units down. New York City counts a fraction of three-quarters or more as a whole unit, so codes differ.
- Unit equivalents. Some codes count other housing types as fractions of a unit. Miami counts a lodging unit as half a dwelling unit and a co-living room as a quarter.
- Bonuses and other limits. Density bonuses, including under state law, can allow more units. Parking, height, and FAR can allow fewer.
Frequently asked questions
How many units per acre is high density?
There is no national standard. Each code sets its own districts, from a few units per acre in single-family districts to well over 100 in urban cores, such as Miami's 150 in its T6 zones.
How do I convert lot area per unit to units per acre?
Divide 43,560 by the lot area required per unit. A requirement of 1,500 square feet per unit equals about 29 units per acre.
Sources
The codes and documents cited on this page were checked on October 20, 2026. Codes are amended often, so confirm the current text before relying on any figure. This page is general information, not legal or design advice.
- National Institute of Standards and Technology: Handbook 44 (2024), Appendix C. One acre equals 43,560 square feet.
- City of Miami: Miami 21 Code, Article 1, Section 1.2, Article 3, and Article 4, Table 2. Definition of density, the land area used, unit equivalents, and density limits by Transect Zone.
- City of Austin: Land Development Code Section 25-2-561. Minimum site area per unit in MF-2. The units-per-acre figure is our arithmetic.
- City of Austin: Land Development Code Section 25-2-492. Maximum dwelling units per lot.
- NYC Department of City Planning: Zoning Resolution Section 23-52. The dwelling unit factor and the rounding rule.
- City of Detroit: Code Chapter 50, Article XIII. Section 50-13-222, lot area excluding rights-of-way.
Related reading
- Floor Area Ratio (FAR) Calculator for US Zoning
Work out how much floor area a lot's FAR limit allows, how many stories that takes at a given footprint or inside setbacks, or the FAR of an existing or planned building.
- Lot Coverage Calculator for US Zoning
Work out building coverage and impervious cover as a share of a lot, how much more footprint or paving a zoning cap allows, and whether setbacks or the cap limit the footprint first.
- Multifamily Site Selection: Finding Land Zoned for Apartments by Right
Which districts allow multifamily by right, how density, height, and parking standards set your unit count, what recent state laws changed, and a parcel search recipe for apartment sites.
- What Is R-4 Zoning? Medium-to-High Density Residential Districts Explained
What R-4 zoning usually allows, why it means mid-rise apartments in Los Angeles and detached houses in Baltimore, how New York, Anchorage, Phoenix, and Detroit define it, and what you can typically build.
- Minimum Lot Size Reform Explained: What Smaller Lot Rules Change for a Subdivision
What minimum lot size rules are, how Texas SB 15, Austin, Houston, and California have lowered them, and what smaller lot minimums change for subdivision yield, approvals, and the limits that remain.