Lot size and unit count are local eligibility questions, not universal ADU thresholds. A city may use lot area, frontage, width, depth, zoning district, existing dwelling type, or a combination. The method of measurement and the units already on the parcel can matter as much as the number shown on a listing.
Use the authority’s parcel record and measurement method
Confirm the parcel boundary, official area, frontage, zone, and existing dwelling count with the responsible authority. A real-estate listing or rounded assessor number is not a substitute for a survey or the measurement method specified by the code. Check whether the rule measures the whole lot, excludes a right-of-way, treats a corner lot differently, or uses a separate frontage definition.
Read thresholds with their exact scope
Portland publishes different lot-area examples by zoning district and distinguishes houses, duplexes, and manufactured homes. Austin’s current Development Services screen lists SF-1, SF-2, and SF-3 zoning and a minimum lot area of 5,750 square feet for its stated ADU screen; the city’s page also says required unit size depends on district and geographic location. These are local examples, not transferable minimums. If your jurisdiction has a state or provincial ADU rule, check how it interacts with the local zone and parcel conditions.
Count units by local definition
Determine what the authority counts as a primary dwelling, accessory dwelling, converted unit, junior unit, or existing legal unit. Some rules cap the combined number of units or allow a different count with a duplex or other primary building. Do not count a shed, suite, or tax-record entry as a legal dwelling without confirming its classification and permit status.
Separate eligibility from buildable space
Meeting a minimum-lot screen does not show that the proposed building fits. Setbacks, height, floor area, lot coverage, access, services, overlays, and building-code requirements are separate checks. Columbus, for example, offers a preliminary zoning-only review that asks for a parcel number and site plan with lot area, unit areas and count, setbacks, coverage, parking, and site geometry to identify possible variance needs; it is not an approval.
For local examples, see the Austin lot-area screen and Winnipeg’s form-specific suite thresholds. Confirm the current rule, parcel measurements, and unit inventory with the authority before drawing a conclusion.