Room Addition Cost Calculator (2026)
Price a ground-floor room addition, from a 12x12 bedroom to a 20x30 family room, using the published low, typical, and high cost per square foot for a room addition, then scale the labor share by your state’s construction wage index. The calculator starts on the room type; switch to a bump-out, suite, or second story any time. Estimate (non-official)
Estimated range at the U.S. median
$43,325 – $124,750
Typical estimate $87,850 ($219.63 per sq ft) Estimate (non-official)
| Hard cost | $40,000–$100,000 (typical $75,000) |
|---|---|
| Foundation adjustment | $0–$0 (typical $0) |
| Systems | $0–$0 (typical $0) |
| Design fees | $3,000–$20,000 (typical $10,313) |
| Permit | $325–$4,750 (typical $2,538) |
Your renovation budget
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| Typical project estimate | – |
|---|---|
| Contingency reserve | – |
| Budget to plan for | – |
| If bids come in at the high end | – |
| Still to save or finance | – |
Get at least three written bids for the same scope, check licensing and insurance, and compare line items rather than totals. Homeowner planning guide
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|---|---|
| Overhead | – |
| Profit | – |
| Contingency | – |
| Bid price | – |
| Gross margin / total markup | – |
| Compared with the market range | – |
Printable estimate details
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Room addition cost by size
Mid-range finish, slab foundation, architect fee on, no bathroom or kitchen, U.S. median construction wage index (1.00). Estimate (non-official)
| Size | Range | Typical | Per sq ft |
|---|---|---|---|
| 200 sq ft | $21,825–$64,750 | $45,194 | $225.97 |
| 400 sq ft | $43,325–$124,750 | $87,850 | $219.63 |
| 600 sq ft | $64,825–$184,750 | $130,506 | $217.51 |
Common room sizes: a 12x12 bedroom is 144 sq ft, a 12x16 is 192 sq ft, a 16x20 family room is 320 sq ft, and a 20x20 is 400 sq ft. Type the square footage into the calculator for your exact size, and add bathroom square footage separately because it uses its own rate.
Types of additions
Each rate is the researched range for that project type. Finish level in the calculator selects the low, typical, or high column. Estimate (non-official)
| Type | Low–typical–high per sq ft | Sources |
|---|---|---|
| Bump-out | $82.50–$200.00 (typical $141.25) Estimate (non-official) | |
| Single-room ground-floor addition | $100.00–$250.00 (typical $187.50) Estimate (non-official) | |
| Primary suite (bedroom + bath) | $297.03–$387.20 (typical $342.11) Estimate (non-official) | |
| Sources disagree. Large conflict: CVV national cost per sq ft is about 2-2.5x HomeGuide's. | ||
| Second-story addition | $150.00–$400.00 (typical $275.00) Estimate (non-official) | |
| Sources disagree. | ||
| Attached garage | $36.70–$90.00 (typical $63.35) Estimate (non-official) | |
| Sources disagree. Sources conflict (Angi ~$30 vs HomeGuide ~$43-$150 derived). Fixr $23,000-$45,000 (no size) not used. | ||
| Sunroom | $100.00–$350.00 (typical $225.00) Estimate (non-official) Single published source. | |
| In-law suite / attached ADU | $100.00–$275.00 (typical $187.50) Estimate (non-official) | |
20x20 home addition cost
A 20×20 addition is 400 sq ft. Using a mid-range room, a slab, no extra bathroom or kitchen, the architect fee on, and a construction wage index of 1.00 (the U.S. median), the range is $43,325 to $124,750, typical $87,850 ($219.63 per sq ft). Estimate (non-official) Choose a state in the calculator to replace the index of 1.00 with that state’s OEWS construction wage index.
Second story vs ground floor
A ground-floor room is typically $187.50 per sq ft ($100.00–$250.00). A second story is typically $275.00 per sq ft ($150.00–$400.00). Estimate (non-official) The second-story choice sets foundation work to none, because the new floor area is over the existing house. See the second story addition calculator or the room addition calculator for size-by-size examples.
Home addition cost per square foot
The type table above is the cost-per-square-foot guide. Bathroom and kitchen square footage inside the addition use their own rates instead of the type rate. The Census figures below are context for new houses, not additions.
| Census region | Median | Average |
|---|---|---|
| Midwest | $194.09 | $202.13 |
| Northeast | $179.30 | $246.26 |
| South | $157.30 | $179.96 |
| West | $176.87 | $213.85 |
Census figure is for new single-family houses, not additions. Relative standard errors are published in the CHARS workbook; this table shows the median and average only.
What affects addition costs in your state
Pick a state in the calculator. The wage table uses the OEWS median hourly wage for that state. The cost formula uses the construction-and-extraction wage index, not these trade rates directly.
| Trade | Median hourly |
|---|---|
| Carpenters | $29.12 |
| Construction laborers | $22.66 |
| Electricians | $30.38 |
| Plumbers | $30.67 |
| HVAC | $29.33 |
Questions
How much does a room addition cost?
A ground-floor room addition typically costs $100.00 to $250.00 per sq ft (typical $187.50). A 400 sq ft room with a slab and architect fees is about $87,850 at the U.S. median wage.
How much does a 12x12 or 20x20 room addition cost?
A 12x12 room is 144 sq ft and a 20x20 room is 400 sq ft. Multiply by the per-sq-ft rate for your finish level, then use the calculator to add a bathroom, foundation type, and your state wage index.
Is a room addition cheaper than a second story?
Per square foot, usually yes: the typical second-story rate is $275.00 per sq ft versus $187.50 for a ground-floor room, but a ground-floor room needs a foundation and lot space.
How much does a 20x20 home addition cost?
A 20 by 20 room is 400 sq ft. At the U.S. median construction wage (index 1.00), mid-range finish, slab foundation, no extra bath or kitchen, and the architect fee on, the range is $43,325 to $124,750 (typical $87,850, $219.63 per sq ft). Estimate (non-official). Pick a state to apply that state’s construction wage index.
How does a second-story addition compare with a ground-floor room?
The researched typical rate is $187.50 per sq ft for a ground-floor room and $275.00 per sq ft for a second story (ranges $100.00–$250.00 and $150.00–$400.00). Estimate (non-official). A second story does not add foundation area in this calculator.
Do the addition prices already include a foundation?
The guides are treated as including a basic slab. Choosing crawl, basement, or pier-and-beam adds the difference versus that slab, times local labor adjustment. Choosing none adds no foundation dollars. That slab assumption is editorial; the guides do not state it.
Why does my state change the addition estimate?
Only the labor share is scaled. With a labor share of 50%, the local factor is 1 minus that share plus that share times the state’s construction wage index (BLS OEWS, all construction and extraction occupations, versus the U.S. median).