ADU Cost Per Square Foot: 2026 Pricing by Size
Quick answer: ADUs cost about $200 to $500 per square foot in 2026. Garage conversions sit at the low end, around $150 to $300. Detached new builds sit at the high end, around $250 to $500. Smaller ADUs often cost more per square foot because the kitchen and bathroom are fixed costs spread over less space.
If you are pricing an ADU, cost per square foot is the fastest way to sanity check a quote. But it can fool you. Here is how it really works, and what common sizes actually cost.
Typical cost per square foot in 2026
These are national ranges. Your city and your finish level move the number a lot. For the full picture on total budget, see our guide on how much an ADU costs.
Why smaller can cost more per square foot
This surprises a lot of homeowners. A tiny ADU often has a higher cost per square foot than a bigger one.
The reason is the kitchen and the bathroom. Those two rooms hold the most expensive work in the whole unit. Plumbing, electrical, cabinets, counters, tile, appliances. A 400 square foot studio needs the same kitchen and bath as an 800 square foot one bedroom. So in the small unit, those fixed costs get spread over less space, which pushes the per square foot number up.
The takeaway. Do not assume going smaller always saves money per foot. Sometimes a slightly bigger unit gives you more space for nearly the same per foot cost.
What common ADU sizes cost
500 square foot ADU
A compact studio or small one bedroom. Plenty for a renter, an office, or aging parents. Expect roughly $100,000 to $200,000 all in for a new build, less for a garage conversion of similar size. The per square foot cost runs high here because of the fixed kitchen and bath.
800 square foot ADU
A comfortable one bedroom or tight two bedroom. This is a popular size because it balances livability and cost. Expect roughly $160,000 to $300,000 for a detached new build, depending on finish and location.
1200 square foot ADU
A full two bedroom with real living space. The most expensive common size, but the best per square foot value because the fixed costs are spread out. Expect roughly $240,000 to $400,000 or more for a detached new build.
How to use cost per square foot
Use it as a gut check, not a final number. When a builder hands you a quote, divide the total by the square footage. If it lands wildly outside the ranges above, ask why. Maybe the lot needs heavy site work. Maybe the finishes are high end. Maybe the quote is off. Either way, you now know to ask.
The only way to get your real number is a builder walking your lot and pricing your project. A garage conversion will price differently than a backyard build. See garage to ADU conversion cost if that is your path.
Frequently asked questions
How much does an ADU cost per square foot in 2026?
About $200 to $500 per square foot all in. Garage conversions run lower at $150 to $300, and detached new builds run higher at $250 to $500.
Why does a small ADU cost more per square foot?
Because the kitchen and bathroom are the most expensive rooms and they cost about the same no matter the unit size. In a small ADU, those fixed costs are spread over fewer square feet.
What size ADU gives the best value?
Larger units like 1000 to 1200 square feet usually offer the best cost per square foot, since the expensive kitchen and bath are spread over more living space.
Does cost per square foot include permits and design?
It can, but always ask. Some builders quote construction only. A true all in number includes design, permits, and site work.
Building ADUs for a living?
If you build ADUs and want a steady flow of homeowners who already understand these numbers, see how ADU marketing for builders works.