Garage & ADU Cost Calculator — Per Square Foot
Budget a detached garage or accessory dwelling unit. Pick the project type and quality, enter the size, and add utilities, a kitchen, and bathrooms — the calculator builds a per-square-foot estimate with design, permit, and contingency, plus a downloadable PDF.
| Item | Basis | Cost |
|---|---|---|
| Run the calculator to see the breakdown | ||
How to use the garage & ADU cost calculator
Four quick steps turn your project type and size into a full build budget — base build, utilities, kitchen and baths, design, permit, and contingency — with an all-in per-square-foot figure and a downloadable estimate.
Pick type & quality
Choose a detached garage, garage + ADU, or full ADU, and a quality tier. The base rate auto-fills — edit it.
Enter the size
Give the total floor area you’re building. For a two-story build, use the combined area of both floors.
Add utilities & rooms
Add a utilities hookup, a kitchen, and bathrooms, then a design percentage, permit, and contingency.
Read results & save a PDF
Get the project total, cost by item, and all-in per ft², with a full breakdown — then download an estimate.
How the project cost is calculated
The build is area × a base rate set by project type and quality; utilities and rooms add on, then a design percentage, permit, and contingency finish the budget. Here is the exact math.
Worked example — 600 ft² detached garage, standard tier, 8% design, $500 permit, 12% contingency
Base build: 600 × $55 = $33,000 (no utilities/kitchen/baths)
Design (8%): $2,640 + permit $500 = soft $3,140
Contingency (12% of $36,140): $4,337
Project total: $33,000 + $3,140 + $4,337
≈ $40,477 all-in — about $67/ft². A full ADU at ~$260/ft² runs far higher.
Garage & ADU cost charts
Handy lookups for base rates by type and tier, build cost by size, and typical add-on and soft costs. These are broad national-average ballparks — editable, and no substitute for a quote and a zoning check.
| Project type | Basic | Standard | Premium |
|---|---|---|---|
| Detached garage | ~$47 | ~$55 | ~$74 |
| Garage + ADU | ~$153 | ~$180 | ~$243 |
| Full ADU | ~$221 | ~$260 | ~$351 |
Base build only (shell + finish), before utilities, kitchen, baths, and soft costs. Basic ×0.85, Premium ×1.35.
| Floor area | Garage | Garage + ADU | Full ADU |
|---|---|---|---|
| 400 ft² | ~$22,000 | ~$72,000 | ~$104,000 |
| 600 ft² | ~$33,000 | ~$108,000 | ~$156,000 |
| 800 ft² | ~$44,000 | ~$144,000 | ~$208,000 |
| 1,000 ft² | ~$55,000 | ~$180,000 | ~$260,000 |
| 1,200 ft² | ~$66,000 | ~$216,000 | ~$312,000 |
Base build only. Add utilities, kitchen, baths, design, permit, and contingency — those push an ADU’s all-in figure well higher.
| Item | Typical range |
|---|---|
| Utilities hookup (ADU) | $10,000–25,000+ |
| Kitchen | varies with cabinets & appliances |
| Bathroom | $8,000–15,000 each |
| Design / plans | 6–12% of build |
| Permit / impact fees | varies widely by jurisdiction |
| Contingency | 10–15% |
A stock or pre-approved ADU plan lowers design cost. Impact and utility fees vary enormously — check locally.
| Factor | Effect |
|---|---|
| Project type | garage < garage+ADU < full ADU |
| Quality tier | Basic ×0.85 → Premium ×1.35 |
| Utilities | big for an ADU (water, sewer, power runs) |
| Kitchen & baths | large lump add-ons |
| Site & foundation | slope, access, soil — use contingency |
Zoning can also cap size, height, and parking — confirm feasibility before you design.
Everything the calculator works out
A project type and a square footage give you a full build budget — base build, add-ons, and soft costs, expressed as an all-in cost per square foot.
Key figures behind the budget
Built for planning a build
From a homeowner’s first budget to a builder’s quick bid, the same calculator turns a project type and size into a number.
Planning a new garage or accessory unit and wants a realistic all-in cost before calling builders.
- Pick type, tier & size
- Add utilities & rooms
- See the all-in per ft²
Weighing an ADU as a rental and wants a build cost to test against local rents and rules.
- Model a full ADU
- Include utilities & a kitchen
- Check zoning before you design
Wants a quick type-and-tier estimate to share, then confirms with a site visit and feasibility review.
- Set your own base rate
- Break out soft costs
- Hand the PDF to the client
7 tips for a realistic garage or ADU budget
A ground-up build has more moving parts than a remodel. These points keep the estimate honest — and remember it’s a ballpark, not a bid.
Garage & ADU cost calculator FAQ
The cost, type, and feasibility questions people ask most before building a garage or ADU.
A detached garage is the cheapest of these per ft² — a shell with foundation, framing, roof, a door, and basic electrical, no kitchen or bath.
At a standard finish, budget around $55/ft². A 600 ft² garage is about $33,000 base build, or roughly $40,000 all-in with design, permit, and contingency — about $67/ft².
Adding living space raises the rate sharply. Site and region move these a lot — get written quotes.
A full ADU — its own kitchen, bath, and HVAC — is the most per ft², commonly around $260/ft² for the base build at a standard finish, before utilities and rooms.
A 600 ft² ADU can reach the low-to-mid six figures once you add a utilities hookup ($10,000–$25,000), a kitchen, bathrooms, design, permit, and contingency. All-in of $300–$400+/ft² is common.
Costs swing widely by region, site, and utility runs — get quotes and a feasibility check.
It depends heavily on type. Rough base-build rates at standard finish: about $55/ft² garage, $180/ft² garage + ADU, $260/ft² full ADU.
Basic runs ~15% less, premium ~35% more. Those are base build only — utilities, kitchen, baths, design, permit, and contingency stack on top, so all-in per ft² ends up higher, especially for an ADU.
Use these as planning ranges, not fixed prices.
They differ by how much habitable space and how many systems are involved.
A detached garage is an unconditioned shell — no kitchen or bath. A garage + ADU adds finished, conditioned living space, so it needs insulation, HVAC, and often a bathroom. A full ADU is a complete independent dwelling with kitchen, bath, and its own systems.
More space and systems mean a higher per-ft² cost — which is why the base rate roughly quintuples from a bare garage to a full ADU.
Beyond size and finish, the biggest swings are utilities and the wet rooms.
Running water, sewer or septic, gas, and electrical to a detached unit can add $10,000–$25,000+, especially with long trenching or a service upgrade. A kitchen and each bathroom are large lump costs on top of the per-ft² build. Site conditions — slope, access, soil, foundation — round out the variables.
That’s why an ADU’s all-in is far more than its base rate alone suggests.
Soft costs are the non-construction items every ground-up project carries: design and engineering, permits, and impact or utility fees.
Design and plans typically run 6–12% of the build; a pre-approved or stock plan lowers it. Permit and impact fees vary enormously — some areas charge little for an ADU, others tens of thousands. A 10–15% contingency covers site and foundation surprises.
The calculator adds a design %, a permit lump, and a contingency so the total reflects real project cost.
A garage or ADU is a permitted, inspected structure — you’ll need building permits, and an ADU also has to satisfy zoning.
Zoning governs whether an ADU is allowed at all and caps size, height, setbacks, lot coverage, and parking. Many areas have loosened ADU rules, but requirements still vary widely by city and county. Before spending on design, confirm your lot qualifies and what limits apply.
Start with a feasibility or zoning check at your local planning department — it can save an expensive redesign.
It can be, but it depends on your numbers. An ADU can generate rental income, house family, and add to a property’s value — but payback depends on build cost, local rents, financing, and how long you hold the property.
Compare the all-in build cost here against realistic local rent and any added home value, and factor in financing and upkeep. In high-rent areas an ADU can pay back reasonably; in lower-rent ones it may be more about lifestyle or family use.
This is a planning estimate, not financial advice — run your own numbers and consult a professional first.
Budget Estimate — Not a Quote: The default rates are broad national averages and vary widely by region, site conditions, foundation, utility runs, and finish level. This calculator produces a type- and size-based budget only — it is not a contractor quote, an appraisal, or financial advice, and it does not design the structure. A garage or ADU is a permitted, inspected build that must meet local building code; an ADU must also satisfy zoning, which can limit size, height, setbacks, and parking or prohibit it entirely. Confirm feasibility and zoning with your local planning department, and get written, itemized quotes from licensed contractors before committing. For planning purposes only.