Worked Estimates and Checklists
How to estimate a renovation step by step: from measurements to a budget range
A step-by-step method to estimate an Australian home renovation, with measurements, rate bands, fixed costs, GST, contingency and outside-contract costs, all worked through.
To estimate a renovation yourself, work in seven steps: define the scope in writing, measure the floor area of each part, choose an illustrative rate band for each part, add fixed costs that do not scale with size, make sure everything is GST-inclusive, add a contingency, and finally add costs that sit outside the builder's contract. The result is a low-to-high range, not a price. Its job is to tell you whether a project is affordable and to give you a yardstick for comparing quotes. Every number below is an illustrative assumption, chosen to make the arithmetic easy to follow.
This is the overview for Worked Estimates and Checklists. Related guides: comparing builder quotes, deposits and progress payments, contingency and variations, GST on renovations, council approval costs and prime cost and provisional sums.
Step 1: write the scope
List every room or element and what happens to it. Be specific about finish level. "New bathroom" is not a scope; "strip to frame, same layout, floor-to-ceiling tiles, wall-hung vanity, frameless screen" is. The written scope becomes the brief you give builders, so they quote the same job.
| Element | Scope (example) | Finish level |
|---|---|---|
| Main bathroom | Strip out, same layout, full height tiles | Mid-range |
| Laundry | New cabinetry, tub and tiles | Budget |
| Living and hallway | Paint, new flooring, LED downlights | Cosmetic |
Step 2: measure
Measure the internal floor area of each part, in square metres. For wet areas, floor area is enough for a planning estimate. For flooring and painting, note wall and ceiling areas too if you want detail. Round up slightly.
Example measurements: bathroom 6 m², laundry 4 m², living and hallway 45 m².
Step 3: choose a rate band for each part
Use one band per part. The renovation cost estimator holds illustrative bands including GST. For a laundry, use the budget bathroom band as a rough proxy, because it has similar trades.
| Part | Area | Band per m² (illustrative) | Low | High |
|---|---|---|---|---|
| Bathroom, mid-range | 6 m² | $4,500 to $7,500 | $27,000 | $45,000 |
| Laundry, budget wet area | 4 m² | $3,000 to $4,500 | $12,000 | $18,000 |
| Cosmetic refresh | 45 m² | $500 to $1,400 | $22,500 | $63,000 |
| Subtotal | $61,500 | $126,000 |
The wide range for the cosmetic refresh reflects how much depends on product choice: a floating floor and basic paint versus engineered timber and new joinery.
Step 4: add fixed costs
Fixed costs do not scale with area. List each one, even if it is a guess.
| Fixed cost (illustrative) | Amount |
|---|---|
| Design advice or drawings | $2,000 |
| Asbestos testing in a pre-1990 home | $600 |
| Switchboard upgrade | $2,400 |
| Skip bins, if excluded from quotes | $1,500 |
| Total fixed | $6,500 |
Running total: $61,500 + $6,500 = $68,000 (low) and $126,000 + $6,500 = $132,500 (high).
If the work needs approvals, add council, certifier and any levy costs here. See council approval costs.
Step 5: check GST
All the bands on this site already include GST. If you priced any item from a trade quote written ex GST, add 10% with the GST calculator. Mixing ex-GST and GST-inclusive numbers is one of the most common estimating errors.
Step 6: add contingency
Choose a percentage based on risk. This illustrative example uses 15% because the house is older and walls will be opened.
- Low: $68,000 x 15% = $10,200, giving $78,200.
- High: $132,500 x 15% = $19,875, giving $152,375.
The contingency calculator does this in one step.
Step 7: add costs outside the contract
These are costs you pay that no builder will quote:
| Outside-contract cost (illustrative) | Amount |
|---|---|
| Two weeks of short-stay accommodation while the bathroom is out | $2,800 |
| Storage of furniture during flooring | $600 |
| New window furnishings after painting | $1,500 |
| Total | $4,900 |
Final planning range: $83,100 to $157,275.
Reading your result
A range this wide is normal at concept stage. It narrows when you fix finish levels and get quotes. Use it three ways:
- Affordability. If even the low figure exceeds your budget, cut scope now, not after quotes.
- Quote yardstick. A quote far below your low figure may exclude items or carry low allowances; one far above may include things you did not ask for.
- Finance. Lenders often want a builder's contract for construction or renovation loans, but your range helps you decide what to apply for.
Common estimating mistakes
- Using a single rate per m² for the whole house when wet areas and living areas differ widely.
- Leaving fixed costs at zero because they are hard to guess.
- Treating contingency as optional.
- Forgetting the costs of living through the work.
- Not updating the estimate when the scope changes.
When to pay for a professional estimate
For an extension, second storey or whole-house renovation, a quantity surveyor can produce a measured cost plan from drawings. That costs money but can save more by showing where the budget goes before you tender the job. A building designer or architect can also help match scope to budget.
FAQ
How accurate is a DIY estimate?
It is a planning range. Accuracy improves as the scope gets more detailed and once you have quotes for the main items.
Should I share my estimate with builders?
Many owners share a budget range rather than a detailed estimate, so builders can tell you early whether the scope fits it.
What contingency should I use?
An illustrative 10% for simple, well-documented work, and 15% to 20% for older homes and structural work. See contingency and variations.
Can I estimate approvals myself?
Roughly, from your council's fee schedule and a certifier's quote. See council approval costs.
Sources
- Australian Building Codes Board — National Construction Code
- Queensland Building and Construction Commission — contract and payment rules in Queensland
- Building Commission NSW, via NSW Government — preparing to build or renovate in NSW
- Building and Plumbing Commission (Victoria) — Victorian building permits and insurance
- Moneysmart — budgeting and borrowing for renovations
