If you are thinking about building an ADU, one of your first questions may be: How big can it be?

The answer depends on the number of bedrooms, your property, and your city or county’s ADU ordinance. Understanding the basic California requirements can help you narrow down your options before choosing a floor plan.

How Big Can an ADU Be in California?

As of September 2026, California homeowners have several ADU size options available. Cities and counties may establish local size standards, but under  California Government Code Section 66321, they must allow at least:

• 850 square feet for an ADU with one bedroom or less
• 1,000 square feet for an ADU with more than one bedroom

State law also supports opportunities for an ADU of at least 800 square feet with four-foot side and rear setbacks, even when certain lot coverage, floor area ratio, or open-space requirements would otherwise apply.

In jurisdictions without a compliant ADU ordinance, a new detached ADU may be up to 1,200 square feet. Local governments can also adopt more flexible standards that allow larger ADUs. These requirements are explained in the California HCD ADU Handbook and California Government Code Sections 66314 and 66325.

With options ranging from compact floor plans to larger multi-bedroom designs, homeowners can explore an ADU size that fits their property, household, and plans for the future. Confirm your local requirements with your planning department before selecting a floor plan.

Choosing the Right ADU Size

At Perpetual Homes ADU, we offer customizable floor plans ranging from one-bedroom models to multi-bedroom homes.

The right size depends on your property and how you plan to use the space. A one-bedroom ADU may provide enough room for an individual or a couple, while a two-bedroom or larger design can offer more space for a family or multigenerational living.

When comparing floor plans, consider the number of bedrooms and bathrooms you need, the available space on your property, site access, existing structures, utility locations, local building requirements, and your project budget. The goal is to find an ADU size and layout that fit your property and needs.

Let’s Find an ADU That Fits Your Property

Perpetual Homes ADU is a Northern California-based prefab ADU and home builder with more than 40 years of experience. We offer customizable floor plans, permit management, financing recommendations, a seven-year ADU warranty, and homes manufactured locally by Skyline Homes in Woodland, California.

Explore our California prefab ADU models and connect with our team to find a size, layout, and design that may work for your property.