← 🏠 Homeowners and DIYers toolkit
Renovation Budget Calculator
Pick your project and work through it in the order you will do it, with the cost of each stage.
Part of the 🏠 Homeowners and DIYers toolkit, with more tools made for the job.
Converting a garage usually needs sign-off under local building rules, and sometimes planning permission or a check of your property deeds. Rules on permits, building regulations and which work needs a qualified person differ by country and place, so check yours before you start.
Plan the conversion
The floor area of the garage lets you see the cost per square metre or foot at the end.
The floor area of the garage
Use this instead of length and width.
Plan it and check the rules
Before any work: drawings, approvals and anything that affects neighbours.
Make the shell sound
A garage is built to keep a car dry. The floor, the front and the structure usually need work first.
Insulate it
Walls, ceiling and floor all need insulating to suit a living space.
Run the electrics, heating and plumbing
Done before the walls are closed up. Electrics, gas and some plumbing need a qualified person in many places.
Plaster, floor and decorate
The finishes that make it feel like a room.
Clear up
Waste, and the things that crop up at the end.
Running it afterwards
Once it is done it can still cost something. This is not part of the cost above.
Your garage conversion, step by step
What each stage adds, and the total.
Type some prices in the steps above and the whole cost appears here, stage by stage.
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Choose what you are planning and give its size. Then work down the page through each stage of the job, typing what each part costs from your quotes and prices. A running total builds as you go, and the summary adds a safety margin.
First-time renovators almost always run over, and it is rarely one big thing. It is a pile of small ones: a skip, fees, a pipe that is not where it should be, a wall that needs more plaster than expected. Working through a project in the order you will do it, one stage at a time, is the best way to catch them, because you picture each step and ask what it needs. The stages here are the usual ones for each kind of project, and the amounts in the boxes are only examples. Replace them with your own quotes.
How it’s worked out
- Step 1, the size: the area of the project, and for some projects a depth or a count, such as the number of raised beds. This lets items be priced by area, volume or number.
- Each stage after that is one part of the job in building order, with its own cost lines. Leave empty any line that does not apply.
- Each stage shows its own total and the total so far, so you can see the cost build up.
- The summary adds every stage, plus a share kept back for surprises. If you leave it empty, 15 percent is used. Common advice is to keep 10 to 20 percent.
- If you give the area, you also see the cost per square metre or foot. Projects with running costs show a yearly figure as well.
A patio of 15 square metres with a 10 cm stone base needs 1.5 cubic metres of stone. With a 10 percent allowance for cuts that is 1.65, and priced at 45 a cubic metre it is about 74, shown in the stone base stage with the rest of that stage's costs.
Common mistakes
- Leaving out the small lines: skip hire, fees, delivery, tool hire and making good afterwards.
- Using one quote and hoping. Get several written quotes, and make sure each covers the same stages.
- Spending the contingency early. It is for things you cannot predict, not upgrades you fancy.
- Skipping a stage because it looks cheap. Groundwork, preparation and finishing are where budgets quietly grow.
Questions
How much contingency should I keep?
Many guides say 10 to 20 percent, and more for older houses where you may find problems behind the walls. The box uses 15 percent if you leave it empty.
What is a typical cost?
It varies enormously by place, size, finish and who does the work, so this tool does not give prices. The numbers in the boxes are examples. Use real quotes.
Does it include labour?
If you pay someone, put their cost in the relevant line. Labour is a large share of many projects, so check it is in your quotes.
Do I need permission for the work?
Often yes for structural changes, new electrics, plumbing or gas, and for conversions. Rules differ by country and place, so check yours before you spend.
Estimates only
These are estimates and general information, not building, safety, legal or professional advice. Materials, coverage, waste and rules vary by product, project and place, so check the maker's instructions and your local rules, and use a qualified person for gas, electrical and structural work.
Rain stopped play. Officially research.