Free Garage Conversion Calculator (+ Guide)

What is a garage conversion calculator?

A garage conversion calculator adds up every cost of turning a garage into living space, from the contractor's quote to the heating.

It shows the total with a contingency, the cost per square foot and what's left of your budget.

How it works

The cheapest of your quotes goes in the total, next to the costs it doesn't cover.

What the building code asks of a converted garage

Once a garage is living space, the 2024 International Residential Code treats it as a room.

• A habitable room must be at least 70 sq ft and at least 7 feet in any direction (R312)
• Its ceiling must be at least 7 feet high (R313.1)
• A bedroom needs an emergency escape window or door, at least 5.7 sq ft open, 24 inches high and 20 inches wide (R319)

Your town may use another edition or its own changes, so ask its building department first, about zoning too.

How to compare contractors' quotes

The Federal Trade Commission gives this advice before you hire anyone.

• Hire only licensed and insured contractors, and check the license with your state or county
• Get several written estimates, each with the work, the materials, the completion date and the price
• Don't automatically pick the lowest bid, and ask why if the estimates differ a lot
• Get a written contract with the contractor's license number and the start and finish dates
• Never pay the full amount up front, and make the final payment only when the work is done

It also warns that a contractor who asks you to get the permits, or who only takes cash, may be running a scam.

How much contingency to add

A contingency is money set aside for what you find once the walls or the ground are open.

HUD requires one on its 203(k) renovation loans: 10% to 20% of the repair costs on a home 30 years or older, and at least 15% when the utilities don't work.

On a newer home, it's up to the lender, to a maximum of 20%.

A worked example

Here's the example the calculator loads: a 400 sq ft garage with 3 quotes of $25,000, $29,000 and $27,000, plus windows, flooring, heating and cooling, paint and permits.

The cheapest quote is $25,000, $4,000 less than the dearest. Your other costs add $9,300, so the project comes to $34,300 before the contingency.

A 10% contingency adds $3,430, for a total of $37,730. That's $94.33 per square foot, and $2,270 left of a $40,000 budget for the garage conversion.

Mistakes to avoid

These are the slips that come up most.

• Forgetting insulation and heating, which a garage never had
• Leaving the garage door's opening without a planned wall
• Skipping the zoning check with your town

Who is the garage conversion calculator for?

It's for anyone turning a garage into a bedroom, an office or a studio, and these tools help around it.

• Square footage calculator – for the room's size
• Flooring calculator – for the floor
• HELOC calculator – if you borrow for it

Check the rules before the quotes, and the conversion is priced for what it must be.