ADU size calculator
ADU Size & Layout Calculator
Drag out a footprint and see the square footage, plus where it lands against the size and fee thresholds that matter in California.
The tool moved, and it grew
Size it, lay it out, furnish it, and see the payback.
The size calculator is now part of the full ADU Designer, with furniture you can move and turn, zoom, and a payback estimate on your own numbers.
Plan the ADU before you build it.
Wondering how big an ADU you can build in Ventura County? Start with a simple footprint, explore a conceptual floor plan, and see how different sizes can work as a real living space. Ventura ADU Specialists can then review your actual property, zoning, site conditions and project requirements before you move forward.
The tool above covers ADU planning, ADU floor plans and ADU size. What it cannot cover is your parcel. ADU design in Ventura County, ADU permits and ADU construction all depend on the property itself, which is why every project we take on starts with property and zoning research rather than a drawing.
Whether you are considering a garage conversion ADU, a detached ADU in the backyard or an attached unit, the same first question applies: what can the property actually take?
Every property is different. The interactive design above is a conceptual planning tool, not a construction drawing or a guarantee that an ADU can be built on your property.
What the thresholds mean
500 square feet. The ceiling for a Junior ADU, which has to sit entirely within an existing or proposed single-family home.
750 square feet of interior livable space. At or below this, an ADU is generally exempt from certain local agency, special district and water corporation impact fees. Above it, those impact fees are generally charged in proportion to the size of the primary dwelling. Different rules can apply to other fees, including school-related fees and utility charges.
800 square feet at 16 feet in height. A baseline that local lot coverage standards generally cannot be used to block, where the unit meets the four-foot side and rear setbacks.
1,000 to 1,200 square feet. Common local ceilings across Ventura County jurisdictions, varying by city and by whether the unit is attached or detached. Several cities also tie an attached unit's size to a percentage of your existing house.
What the calculator cannot tell you
It draws a rectangle. It does not know your setbacks, your lot coverage, your easements, where your sewer lateral runs, your parking requirement or your jurisdiction's ordinance. Those are what actually decide the size of the unit you can build, and they are what we research before we design anything.
That's just a rectangle. We'll tell you whether it fits your actual lot.
Size
From a rectangle to a real footprint.
Send us the address and we will tell you what the parcel will genuinely carry.