ADU Cost Calculator: How to Use It and Read Your Estimate

Our free ADU cost calculator gives you an instant construction estimate. It works from two things: the size of the ADU in square feet and the finish level you want. The estimate is size multiplied by our flat construction rate for that finish level: $275 per square foot for basic, $300 for mid-range and $325 for luxury. The result is a fast, realistic starting number for building an ADU in Los Angeles, Glendale, Burbank, Pasadena and nearby areas.

This guide walks you through the choices behind the estimate, shows worked examples, explains what that estimate covers and what it does not, and lays out how to go from a calculator number to a fixed quote you can actually plan around. If you want to try it while you read, open the ADU cost calculator in another tab and follow along.

The formula behind the calculator

There is no mystery math. Our construction pricing is a flat rate per square foot, set by the finish level you choose:

Basic: $275 per sq ft
Mid-range: $300 per sq ft
Luxury: $325 per sq ft

The estimate is simply size x rate for the chosen finish level. That is why the calculator can give you an answer instantly. Most LA ADUs land between roughly $150K and $325K to build, depending mostly on how big the unit is and which finish level the homeowner picks.

A flat rate has a practical benefit for you as a homeowner: you can see exactly how much each decision moves the number. Add 100 square feet and you know what that costs. Step up a finish level and you know what that costs. You are not guessing at how a contractor bundled things.

Step by step: getting a useful estimate

Step 1: Settle on a size

Size is the biggest lever in your estimate. Think about the interior square footage you want. If you do not have a number in mind, browsing our ADU floor plans is a good way to get one. We have 39 plans, and seeing real layouts helps you understand what a given square footage actually feels like (how many bedrooms fit, whether you get a full kitchen, where storage goes).

A tip from the field: homeowners often start bigger than they need. Before you lock in a size, ask who will live there and for how long. A one-bedroom for a parent or a renter may be very comfortable at a smaller size, and every square foot you skip comes straight off the estimate.

It also helps to know what kind of unit you are leaning toward: a detached backyard ADU, an attached ADU, a garage conversion or a junior ADU inside your existing home. The calculator works from size and finish level, but the type of unit shapes the scope and site questions that come up later. If you are undecided, our guide on choosing the right type of ADU build can help.

Also keep in mind that size limits for ADUs are set by state and local rules, and those rules change. The calculator will happily price any size you type in, but what you can actually build depends on your lot and current regulations. For the state overview, see the California Department of Housing and Community Development ADU page, or ask us during a consultation.

Step 2: Choose a finish level

Finish level sets your per-square-foot rate. In broad terms:

Basic ($275/sq ft): solid, durable finishes. A good fit for rentals and budget-focused builds.
Mid-range ($300/sq ft): upgraded selections that many homeowners choose when family will live there or when they want a rental to stand out.
Luxury ($325/sq ft): higher-end selections for owners who want the ADU to feel like a premium home.

Labels only tell you so much, so when you request a fixed quote, ask what specific items each finish level includes.

Step 3: Read your result

The number you see is a construction estimate. Treat it as your planning baseline: good enough to decide whether the project fits your budget, compare sizes and finish levels, and start a financing conversation. It is not yet a fixed quote, and the next sections explain why.

Worked examples using our rates

Here is how the math plays out on a few typical projects.

Example 1: A 500 sq ft mid-range ADU

500 sq ft x $300 per sq ft = $150K in construction. This is a common size for a compact one-bedroom or a generous studio, and it sits at the lower end of the range most LA ADUs fall into.

Example 2: A 600 sq ft mid-range ADU

600 sq ft x $300 per sq ft = about $180K in construction. That extra 100 square feet over Example 1 can be the difference between a tight one-bedroom and one with room for a real dining area or a second closet.

Example 3: A 1,000 sq ft luxury ADU

1,000 sq ft x $325 per sq ft = closer to $325K in construction. This is the top of the typical range: a larger, two-bedroom style unit with luxury finishes.

What the examples teach

Notice that size moves the number much more than finish level does. Going from basic to luxury changes the per-foot rate by a modest amount, while adding or removing a few hundred square feet changes the total a lot. If your estimate comes in higher than you hoped, try trimming square footage before you drop to a lower finish level. You might keep the finishes you love in a slightly smaller, smarter layout. Our guide to building an ADU on a budget covers more ways to bring the number down.

Want to test your own scenario? Run your numbers in the calculator and try two or three sizes side by side.

What a construction estimate includes, and what it does not

This is where most confusion comes from, so it is worth being direct. The calculator estimates construction: building the ADU at the size and finish level you chose. That is the largest piece of an ADU budget, but it is not always every dollar you will spend.

Items that can sit outside a simple per-square-foot construction number, and that you should ask about when you get a fixed quote, include:

City and agency fees: plan check, permit and other fees are set by your city or agency, vary by jurisdiction and change over time.
Utility work: whether your existing electrical service can support another unit, and how far sewer, water and gas lines have to run, depend on your property.
Site conditions: slopes, poor soil, tight access for equipment, trees or existing structures that need attention.
Scope specific to your ADU type: a garage conversion, for example, raises questions about the condition of the existing slab, walls and roof.
Things outside the unit: landscaping, fencing, extra hardscape or outdoor features you may want later.

None of this means the calculator is off. It means the calculator does not know your lot yet. Two identical 600 sq ft ADUs can have different total budgets because one sits close to the main house's utilities on a flat lot and the other does not. For a fuller picture of what drives total ADU budgets in LA, read our builder's breakdown of ADU costs in Los Angeles.

Using the calculator to make real decisions

A calculator is most useful when you use it to compare options, not just to get one number. A few practical ways to put it to work:

Set a ceiling first. Decide the most you are comfortable spending, then work backward to the size and finish level that fit.
Compare two sizes at the same finish. This shows you what each extra room really costs.
Compare finish levels at the same size. This helps you decide if upgraded finishes are worth it for your purpose (a parent's home versus a rental, for example).
Bring the number to your lender. A grounded construction estimate makes financing conversations more productive. For financing specifics, talk to a lending professional, and for tax questions, a qualified tax professional.

From calculator number to fixed quote

The calculator gets you in the right range. A fixed quote is the exact number you plan around. When you are ready, reach out to request one. The more clearly you can describe your project, the more productive that conversation will be.

Things worth having ready when you ask for a fixed quote:

Your calculator result, including the size and finish level you used.
The type of ADU you are considering and roughly where it would go on your lot.
A floor plan or two you like, if you have browsed our 39 plans.
What you know about your property: slope, access from the street, location of existing utilities and any existing structures like a garage.
Your goals: housing family, renting, a home office, or something else.

Because we handle design, permits and construction under one team, you are not coordinating separate designers, permit expediters and builders. That helps reduce the hand-off gaps where costs and delays tend to creep in. On the permit side, a well-prepared package typically moves through plan check in weeks per correction cycle rather than months. Most permit delays come from incomplete submittals and slow responses to plan-check corrections, so a complete submittal and quick responses matter. Every city and project is different, though, so we cannot promise a specific timeline. You can check your local building department, such as LADBS in the City of Los Angeles, for current requirements.

Common mistakes when reading a calculator estimate

Treating it as a final price. It is a construction estimate, not a fixed quote.
Forgetting site-specific costs. Utilities, access and site conditions are real and vary by lot.
Assuming any size is allowed. Rules on size, setbacks and placement depend on current law and your lot.
Choosing finish level by label alone. Ask to see what is actually included before deciding.
Comparing it to bids that hide scope. When you compare numbers, make sure they cover the same work.

Frequently asked questions

How accurate is the ADU cost calculator?

It uses the same flat per-square-foot rates we build at, so the construction math is real. What it cannot see is your specific lot, utilities and local fees, which is why the next step is a fixed quote.

What do the $275, $300 and $325 rates mean?

They are our flat construction rates per square foot for basic, mid-range and luxury finish levels. Multiply your size by the rate for your chosen level to get the construction estimate.

Does the estimate include permits and city fees?

The calculator estimates construction. Permit and agency fees are set by your city, vary by location and change over time, so ask about them when you request a fixed quote.

Why does size change the estimate more than finish level?

The finish levels are close together on a per-foot basis, while size multiplies the whole rate. Trimming a few hundred square feet usually saves more than stepping down a finish level.

How do I get a fixed quote?

Contact us through a free consultation and share your size, finish level, ADU type and what you know about your property. Homeowners get a fixed quote for their specific project.

Ready to see your number? Start with the free ADU cost calculator, browse our floor plans for size ideas, then book an ADU consultation to turn your estimate into a fixed quote. You can also reach us at (866) 429-1440, Mon-Sat, 9am-6pm PT.