Garage Conversion & ADU Cost Calculator
Budget a garage conversion or ADU from the floor area and $/sq ft you enter, plus kitchen/bath/HVAC add-ons and a contingency.
Calculator
Converting a 400 sq ft garage (or an ADU budget) is about $55,200.00 with your add-ons and a 15% buffer. ADUs need permits, and plumbing/electrical/HVAC work belongs to licensed pros.
Converting a garage into living space — a bedroom, an office, or a full accessory dwelling unit (ADU) — reuses an existing slab and walls, which is why it is often cheaper per square foot than a ground-up addition. The base conversion (insulation, drywall, flooring, replacing the garage door with a wall and windows, basic electrical) is estimated on your $/sq ft; a kitchen, bathroom or new HVAC that turns it into an ADU is added as line add-ons, and a contingency covers the surprises.
An ADU is a self-contained unit with its own kitchen and bath, so its add-ons and permitting are heavier than a simple room conversion — enter figures that match the scope you plan.
Formula
Base conversion plus your add-ons, then a buffer:
subtotal = area × your $/sq ft + kitchen/bath/HVAC add-onstotal = subtotal × (1 + contingency%)
The $/sq ft is the base conversion rate you enter; the add-ons capture the ADU-making items (a kitchenette, a bathroom, a dedicated HVAC system) so the base rate stays a clean comparison. The contingency (10–20%) absorbs slab, moisture and code surprises.
Worked example
Take a 400 sq ft garage at a $120/sq ft conversion rate, with $10,000 of kitchen/bath/HVAC add-ons (and, for a clean comparison, no contingency in this check):
subtotal = 400 × $120 + $10,000 = $58,000total = $58,000 × 1.00 = $58,000
So the base ADU budget is about $58,000. Add a realistic 15% contingency and it becomes $66,700 — the buffer you set aside for the unknowns a conversion tends to uncover.
Garage conversions and ADUs
Reusing the slab, foundation and walls is what makes a conversion economical, but garages bring their own issues: slab height and slope, insulation and moisture, and bringing electrical and any plumbing up to habitable-room code. Turning the space into an ADU adds a kitchen, a bathroom and often a separate HVAC system — the add-ons that dominate the budget — plus stricter permitting and sometimes parking or utility requirements.
All of this is licensed, permitted work: plumbing, electrical, HVAC and any structural changes need licensed professionals, a permit and inspections. ADU rules vary widely by jurisdiction — confirm eligibility and code with your local building department first.
When you compare conversion quotes, keep the base rate and the add-ons apart: two bids can look far apart simply because one folds the kitchenette and HVAC into the $/sq ft while the other lists them separately. Entering the base conversion as a rate and the ADU-making items as add-ons here lets you line the bids up on the same terms, and the contingency reminds you to hold money back for the slab, drainage and code surprises that garages so often hide.
Frequently asked questions
How much does it cost to convert a garage?
A base conversion is your $/sq ft times the floor area, plus any kitchen, bath or HVAC add-ons and a contingency. In the example, 400 sq ft at $120/sq ft with $10,000 of add-ons is about $58,000 before contingency. Use rates from your own quotes.
What is an ADU and how is it budgeted?
An accessory dwelling unit is a self-contained living space with its own kitchen and bathroom. Budget the base conversion on $/sq ft, then add the kitchen, bath and HVAC as line add-ons — those extras, plus heavier permitting, are what separate an ADU from a simple room conversion.
What add-ons should I include?
Anything beyond the base conversion: a kitchenette or full kitchen, a bathroom, a dedicated heating and cooling system, upgraded electrical service, or utility separations for an ADU. Keeping them separate lets you compare the base $/sq ft cleanly across quotes.
Do I need a permit to convert a garage?
Yes. Making a garage habitable involves insulation, electrical, often plumbing and HVAC, and sometimes structural changes — all permitted, inspected work. ADUs face additional zoning, parking and utility rules that vary by city. Confirm everything with your local building department before starting.
Why include a contingency on a garage conversion?
Because garages hide problems: an out-of-level or cracked slab, poor drainage, missing insulation, and electrical or code work that only surfaces once you open things up. A 10–20% contingency means a surprise draws down your buffer instead of blowing the budget.