Home Addition Square Footage Cost Calculator
ANA›Life Services Authority›National Calculator Authority›Home Addition Square Footage Cost Calculator
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Home Addition Square Footage Cost Calculator
Estimate the total cost of a home addition based on square footage, addition type, finish quality, and regional cost factors.
Square Footage of Addition (sq ft)
Addition Type
Standard Room Addition Master Suite / Bedroom with Bath Sunroom / Enclosed Porch Kitchen Expansion Garage Addition Second Story Addition Basement Addition
Finish Quality
Basic / Economy Standard / Mid-Range Premium / High-End Luxury / Custom
Regional Cost Factor
Low Cost Region (e.g. rural Midwest/South) Average U.S. Region Above Average (e.g. mid-size metro) High Cost Region (e.g. NYC, SF, Boston)
Include Permit & Design Fees?
Yes — add ~12% for permits, plans & engineering No — exclude permit & design fees
Calculate
function homCalc() { var sqft = parseFloat(document.getElementById('hom-sqft').value); var typeM = parseFloat(document.getElementById('hom-type').value); var qualM = parseFloat(document.getElementById('hom-quality').value); var locM = parseFloat(document.getElementById('hom-location').value); var permitM = parseFloat(document.getElementById('hom-permit').value);
var resultDiv = document.getElementById('hom-result'); resultDiv.style.display = 'block';
// Validation if (isNaN(sqft) || sqft 5000) { resultDiv.className = 'calc-result calc-error'; resultDiv.innerHTML = '⚠ Please enter a square footage between 50 and 5,000 sq ft.'; return; }
// Base cost per sq ft (national average for standard room addition, mid-range finish) var BASE_COST_PER_SQFT = 150; // USD per sq ft
// Core construction cost var constructionCost = sqft * BASE_COST_PER_SQFT * typeM * qualM * locM;
// Permit & design fees (percentage of construction cost) var permitFees = constructionCost * permitM;
// Total cost var totalCost = constructionCost + permitFees;
// Cost per sq ft (effective) var costPerSqft = totalCost / sqft;
// Low / high range (+/- 15%) var lowCost = totalCost * 0.85; var highCost = totalCost * 1.15;
function fmt(n) { return '$' + n.toLocaleString('en-US', {minimumFractionDigits: 0, maximumFractionDigits: 0}); }
resultDiv.className = 'calc-result calc-success'; resultDiv.innerHTML = '### Estimated Home Addition Cost ' + '' + 'Square Footage' + sqft.toLocaleString() + ' sq ft' + 'Base Construction Cost' + fmt(constructionCost) + '' + (permitM > 0 ? 'Permit & Design Fees (12%)' + fmt(permitFees) + '' : '') + 'Effective Cost per Sq Ft' + fmt(costPerSqft) + ' / sq ft' + 'Total Estimated Cost' + fmt(totalCost) + '' + 'Typical Range (±15%)' + fmt(lowCost) + ' – ' + fmt(highCost) + '' + ''; }
#### Formula
Construction Cost = Square Footage × $150 (base/sq ft) × Addition Type Multiplier × Quality Multiplier × Regional Cost Multiplier Permit & Design Fees = Construction Cost × 0.12 (if selected) Total Cost = Construction Cost + Permit & Design Fees Effective Cost per Sq Ft = Total Cost ÷ Square Footage Typical Range = Total Cost × 0.85 to Total Cost × 1.15
Multipliers used:
- Addition Type: Standard Room (1.00), Master Suite (1.20), Sunroom (0.85), Kitchen (1.35), Garage (0.70), Second Story (1.50), Basement (0.60)
- Quality: Basic (0.75), Standard (1.00), Premium (1.40), Luxury (1.85)
- Region: Low (0.85), Average (1.00), Above Average (1.20), High Cost (1.45)
#### Assumptions & References
- The national average base cost of $150 per sq ft for a standard mid-range room addition is derived from HomeAdvisor, Remodeling Magazine's Cost vs. Value Report, and the National Association of Home Builders (NAHB) data.
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