850 sq ft City cap, 800 sq ft state path
Rancho Cordova's code caps a detached ADU at 850 sq ft with one bedroom or 1,000 sq ft with more, with 4 ft side and rear setbacks and the zone's front setback. State law separately lets a new detached ADU of up to 800 sq ft with 4 ft side and rear setbacks be approved ministerially (Gov. Code 66323). Our free check fits that 800 sq ft path; a larger unit under the City's limits is for a licensed designer to confirm against the zone.
City of Rancho Cordova ADU FAQ (Code 23.901.060); Gov. Code 66323(a)(2)