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.
Example: with Room type Bedroom / living space ($140/sq ft) · Length 16 ft · Width 16 ft · Your region i United States (average) → Estimated cost: $35,840.
- Low estimate$30,464
- High estimate$44,800
- Cost per sq ft$140/sq ft
Computed by the calculator below using its default values. Change any input to see your own numbers.
Addition size
\ud83c\udfd7\ufe0f Get home-addition quotes from local pros
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.
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.