Zoning Density Calculator
Calculate maximum units per acre based on zoning code density limits and minimum lot sizes.
About this calculator
This calculator applies two independent zoning constraints and takes whichever one is more restrictive. Units (Density Limit) is Total Site Acreage multiplied by Max Units per Acre, rounded down -- a pure gross-density cap that doesn't care about lot size at all. Units (Lot Size Limit) instead divides the net buildable area (Total Site Acreage after the Net-to-Gross Ratio deduction for roads, open space, and other non-buildable land) by Minimum Lot Size -- a pure per-unit-footprint cap that doesn't care about the density limit at all. Max Allowed Units is the smaller (governing) of those two, which is why raising Minimum Lot Size never changes Units (Density Limit), and raising Max Units per Acre never changes Units (Lot Size Limit) -- they're calculated on entirely separate constraints.
Effective Density then re-expresses Max Allowed Units as a units-per-acre figure using the ORIGINAL total acreage (not the net buildable acreage), while Net Density uses net buildable acreage instead, so the two density figures will differ whenever Net-to-Gross Ratio is below 100%. Max Building Footprint divides total buildable square footage by Number of Stories, so a taller building spreads the same total floor area across a smaller ground footprint. This tool does not model height limits, setback requirements, parking minimums, open space set-asides, or affordable housing density bonuses that many jurisdictions layer on top of a base density and lot-size limit.
Inputs
Results
Max Allowed Units
84
Effective Density
5.6 DU/acre
How to Use This Calculator
- Enter Total Site Acreage and Maximum Units per Acre from the zoning code.
- Set Minimum Lot Size in square feet as an additional constraint.
- Enter Net-to-Gross Ratio % — the share of gross area that is net buildable after infrastructure deductions.
- Set Average Unit Size in square feet and Number of Stories.
- Review Max Allowed Units — the lesser of the density-based and lot-size-based limits.
- Use Effective Density in your pro forma and compare against market-rate development in the area.
How the result changes with Total Site Acreage
| Total Site Acreage | Max Allowed Units | Effective Density |
|---|---|---|
| 7.5 | 42 | 5.6 DU/acre |
| 11 | 62 | 5.64 DU/acre |
| 23 | 130 | 5.65 DU/acre |
| 38 | 215 | 5.66 DU/acre |
What each input means
- Total Site Acreage
- Total site area in acres.
- Max Units per Acre
- Maximum dwelling units per acre allowed by zoning.
- Minimum Lot Size
- Minimum lot size required by zoning code.
- Net-to-Gross Ratio
- Percentage of gross area that is net buildable (after roads, open space).
- Average Unit Size
- Average building area per unit.
- Number of Stories
- Number of stories for building footprint calculation.
How this is calculated
Worked example, using the default values
- Identify Input Parameters6 parametersTotal Site Acreage = 15, Max Units per Acre = 8, Minimum Lot Size = 5000, Net-to-Gross Ratio = 65, Average Unit Size = 1800, Number of Stories = 2 = 6 input(s) provided
- Calculate Max Allowed UnitsMax Allowed Units84 = 84
- Calculate Effective DensityEffective Density5.6 = 5.6
- Calculate Units (Density Limit)Units (Density Limit)120 = 120
- Calculate Units (Lot Size Limit)Units (Lot Size Limit)84 = 84
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Does raising Minimum Lot Size change Units (Density Limit)?
No. Units (Density Limit) is calculated purely from Total Site Acreage and Max Units per Acre -- Minimum Lot Size plays no role in that specific figure. It only affects Units (Lot Size Limit), the separate constraint that Max Allowed Units compares it against.
Why does the calculator take the lower of the two unit counts?
Real zoning codes typically impose multiple independent limits simultaneously -- a project must satisfy all of them, not just its favorite one. Max Allowed Units reflects that by taking whichever constraint, density or lot size, produces the smaller number, since that's the one that actually governs how many units the site can legally support.
What's the difference between Effective Density and Net Density?
Both divide Max Allowed Units by an acreage figure, but Effective Density uses the total gross site acreage you entered, while Net Density uses the net buildable acreage after subtracting the Net-to-Gross Ratio's share for roads, open space, and infrastructure. Net Density will always be a higher number than Effective Density whenever Net-to-Gross Ratio is below 100%.
Does adding more Stories increase the number of units I can build?
No. Number of Stories only affects Max Building Footprint, which divides the total buildable square footage across however many floors you specify -- it doesn't change Max Allowed Units, which is set entirely by the density and lot-size constraints. More stories means a smaller ground footprint for the same unit count, not more units.
What zoning constraints does this calculator leave out?
It models only base density (units per acre) and minimum lot size. It doesn't account for height limits, required setbacks from property lines, parking minimums, mandatory open space set-asides, or density bonuses many jurisdictions offer for including affordable units -- all of which can further constrain (or in the case of bonuses, increase) what a site can actually support.
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