OneTaskBy Tim King · Updated
Renovation Cost Calculator
Budget From Floor Area and Price Per Square Metre, Plus Fittings, Fees and Contingency
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How the Renovation Cost Calculator works
This renovation cost calculator builds a budget for a renovation, loft conversion or extension from the floor area and the build price per square metre or square foot that local builders quote you. It adds fixtures and fittings, design and permit fees and a contingency, and returns the total and the all-in cost per unit of floor area. It has no built-in rates; get local quotes.
Builders often give ballpark prices per square metre or square foot, and those figures swing widely with the region, the spec and whether the work is structural. Kitchens and bathrooms are usually priced separately because the units, sanitaryware and tiling can cost as much as the building shell around them.
How the renovation cost calculator works
The formula is: building = area × rate; subtotal = building + fixtures; fees = subtotal × fee %; contingency = (subtotal + fees) × contingency %; total = subtotal + fees + contingency. For example, 20 m² at 2,000 a square metre is 40,000, plus 8,000 of fixtures, 4,800 of fees at 10% and 7,920 of contingency at 15%, a total of 60,720 or 3,036 per m². A second example: the same job at 3,000 per m² totals 85,008.
Fees cover architects or designers, structural engineers, planning and building control; 10–15% of the build is a common allowance. Keep at least a 10–20% contingency, more on older houses, where opening up walls and floors often reveals work nobody could price. Ask how many weeks the builder expects the job to take, because VAT or sales tax, temporary accommodation and storage are extra and not included here.
Total renovation cost by floor area and build rate (10% fees, 15% contingency, no fixtures)
| Floor area | At 1,000 per unit | At 2,000 per unit | At 3,000 per unit |
|---|---|---|---|
| 5 | 6,325 | 12,650 | 18,975 |
| 10 | 12,650 | 25,300 | 37,950 |
| 15 | 18,975 | 37,950 | 56,925 |
| 20 | 25,300 | 50,600 | 75,900 |
| 25 | 31,625 | 63,250 | 94,875 |
| 30 | 37,950 | 75,900 | 113,850 |
| 35 | 44,275 | 88,550 | 132,825 |
| 40 | 50,600 | 101,200 | 151,800 |
| 45 | 56,925 | 113,850 | 170,775 |
| 50 | 63,250 | 126,500 | 189,750 |
| 55 | 69,575 | 139,150 | 208,725 |
| 60 | 75,900 | 151,800 | 227,700 |
| 65 | 82,225 | 164,450 | 246,675 |
| 70 | 88,550 | 177,100 | 265,650 |
| 75 | 94,875 | 189,750 | 284,625 |
| 80 | 101,200 | 202,400 | 303,600 |
| 85 | 107,525 | 215,050 | 322,575 |
| 90 | 113,850 | 227,700 | 341,550 |
| 95 | 120,175 | 240,350 | 360,525 |
| 100 | 126,500 | 253,000 | 379,500 |
FAQ
How do I estimate the cost of a renovation?
Measure the floor area, get a build price per square metre or square foot from two or three local builders, add a separate figure for kitchens and bathrooms, then add fees and a contingency. Use the total to set your budget before you ask for detailed written quotes.
How much contingency should I allow for a renovation?
Allow 10% for a simple, well-planned job on a newer home and 20% or more for older properties or structural work. Hidden problems such as rotten joists, old wiring or poor foundations are the usual reason renovations go over budget.
Are design and permit fees included in a builder's price?
Usually not. Architects, structural engineers, planning applications, building control and party wall surveyors are normally paid separately. Ask each builder exactly what their price includes and excludes before comparing quotes.
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