ADU Feasibility Calculator
Several states now require cities to approve accessory dwelling units that meet objective standards. Enter your ZIP code and your proposed unit size to see what the statute in your state guarantees, which protections it provides, and what is still decided by your local planning department.
States with a verified statutory entry
Every entry below is drawn from a verified statutory citation with the date it was retrieved. Where a statute sets no statewide size figure, the size column is left open rather than filled with an estimate.
| State | Requires ADUs | Units required | Size the state guarantees | Detached guarantee |
|---|---|---|---|---|
| California | Yes | 1 | 800 sq ft | 1,200 sq ft |
| Massachusetts | Yes | 1 | 900 sq ft | — |
| Washington | Yes | 2 | Set locally | — |
| Oregon | Yes | 1 | Set locally | — |
| Arizona | Yes | 2 | Set locally | — |
| Maine | Yes | 1 | Set locally | — |
| Vermont | Yes | 1 | Set locally | — |
| New Hampshire | Yes | 1 | Set locally | — |
| Rhode Island | Yes | 1 | Set locally | — |
| Connecticut | Yes | 1 | Set locally | — |
| Montana | Yes | 1 | Set locally | — |
| Colorado | Yes | 1 | Set locally | — |
| Nevada | Yes | 1 | Set locally | — |
| Maryland | Yes | 1 | Set locally | — |
| Arkansas | Yes | 1 | Set locally | — |
| Utah | Yes | 1 | Set locally | — |
| Virginia | Yes | 1 | Set locally | — |
| Florida | No mandate | — | Set locally | — |
17 of 18 entries carry a statewide mandate. Read the full requirements for each state on the accessory dwelling unit rules page, or use the yard rules checker for other project types.
Frequently asked questions
Is the size the calculator shows the maximum I am allowed to build?
No. Statutory sizes are floors, not ceilings. A statute such as California's requires a city to approve a unit up to at least that size without a discretionary hearing; it does not stop the city from allowing more. The calculator compares your proposal with what the state guarantees, then tells you when the answer depends on local standards.
Why does the calculator have no size figure for some states?
Several state statutes require local governments to allow an accessory dwelling unit but do not set a statewide size figure, leaving that to the local ordinance. Rather than invent a number, the calculator says plainly that the state guarantees the use and that the size is set locally.
Which states does the calculator cover?
It covers the states where we have verified a statutory citation. Where a state has no published entry, the tool says so and falls back to the local verification questions instead of guessing.
Does state law override my city or my HOA?
A statewide statute usually sets a floor for what local governments must allow, while your city or county can still apply objective standards such as setbacks, height and utility connections. Association covenants are a separate system, and some statutes void covenants that prohibit accessory dwelling units. Confirm both.
ZoneFig provides general reference information, not legal advice. Yard and zoning rules are adopted locally, so the only binding answer for your address comes from your city, town or county planning and building department. Typical thresholds shown here describe patterns across many jurisdictions and are not the rule at any specific property.