Room Addition Cost Calculator
Estimate adding on to your home. Pick the room type, size, story and region to see a cost range and per-square-foot price.
Addition size
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Get quotesWhat an addition really costs
Bedrooms and living spaces are cheapest per square foot; bathrooms and kitchens cost much more (plumbing, electrical, cabinetry). A second story adds structural cost. Permits and finishes drive the spread.
How it’s calculated & sources
Cost = area (length × width) × per-sq-ft rate for the room type × placement factor. Estimates are then scaled by a regional construction-cost factor for your area (U.S. average = 1.00).
Cost ranges from 2025–26 national home-improvement data (HomeAdvisor, Angi, Fixr and industry guides); regional factors approximate RS Means-style city cost indices. National average addition \u2248 $50,000 \u2014 roughly $80\u2013250/sq ft; a 20×20 room runs $50k\u2013$100k.
Results update as you type and are estimates, not a quote — site conditions, permits, and finishes move the final number. Verify with local pros.
Worked example
A 16×16 ground-level bedroom addition (256 sq ft) runs about $35,800 nationally (~$140/sq ft).
Frequently asked questions
Why are kitchens and baths so much more?
They add plumbing, wiring, cabinetry, tile and fixtures on top of the shell.
Is a second story cheaper?
Usually not \u2014 it needs reinforcement and is more disruptive.
How does region change it?
The estimate scales by a regional cost factor for your area.