Calculator
Room Addition Cost Calculator
Enter the room dimensions, finish, foundation, and state to get an instant range with a breakdown. The calculator uses the same rates as the main calculator, so results match across pages.
Cost per square foot by addition type and finish
| Addition type | Economy | Standard | Premium |
|---|---|---|---|
| Room / Bedroom | $80–$130 | $130–$200 | $200–$350 |
| Kitchen Extension | $150–$220 | $220–$350 | $350–$500 |
| Bathroom | $200–$250 | $250–$350 | $350–$500 |
| Sunroom | $100–$150 | $150–$225 | $225–$350 |
| Second Story | $200–$300 | $300–$450 | $450–$600 |
| Attached Garage | $50–$80 | $80–$120 | $120–$175 |
| ADU / In-Law Suite | $150–$200 | $200–$300 | $300–$450 |
Ranges are planning figures per square foot before foundation and optional features. The calculator below applies the same midpoints: for example, a Standard room addition uses $165 per square foot at the national average.
Tip: measure inside the planned footprint, and decide the finish before comparing bids. See also the 20×20 room addition cost guide.
Planning estimate only, based on 2026 cost data. It is not a quote. Get itemised bids from licensed local contractors before building, and set aside a 10–20% contingency for permits, design fees, and site surprises.