How do you build a renovation budget, room by room?
A renovation budget only becomes something you can trust once it is built on measured areas instead of a guess. Here is the method: measure first, set prices per square metre afterwards, and add a buffer on top.
Short answer: Build the budget in two steps. First: measure each room — floor area, wall area, and ceiling area if relevant — so you have a figure, not a guess. Next: set a price per square metre or per unit for each item (paint, flooring, tiling) and multiply by the measured area. Finally, add a buffer of typically 10–20% on top for unforeseen costs. A budget with no measurements behind it is a wish, not a budget.
Why the budget should be built on measurements, not a guess
It is tempting to estimate "the room is probably about 15 square metres" and calculate from there. The problem is that the error in a guess is rarely small — a room you think is 15 m² can easily turn out to be 12.5 or 17.8 m² in reality, and that difference feeds straight through to how much paint, flooring or tile you order. A budget built on a guess is therefore not a budget with a small margin of uncertainty — it is a guess with a spreadsheet wrapped around it.
The solution is to measure first: the floor area with a tape measure or a survey app, the wall area minus windows and doors, and the ceiling area if it needs painting or insulating. Once you have those figures, the rest of the budget is a simple calculation.
A concrete example: a budget for three rooms
Say you are renovating a living room, kitchen and bathroom, and you have measured the following areas:
- Living room: floor 22.0 m², wall area to be painted 58.0 m².
- Kitchen: floor 11.5 m², wall area for splashback tiling 4.0 m².
- Bathroom: floor 5.5 m², wall area for tiling 21.0 m².
With quotes of £8/m² for paint, £60/m² for new timber flooring laid, and £85/m² for tiling including tiles, the sum looks like this: living-room paint 58.0 × £8 = £464, living-room floor 22.0 × £60 = £1,320, kitchen tiling 4.0 × £85 = £340, bathroom tiling 21.0 × £85 = £1,785. Total for the four items: £3,909. Add a 15% buffer on top for unforeseen costs: roughly £4,495. The figures in the example are illustrative — always get your own quotes, but the method — measure, multiply, add a buffer — is the same whatever prices you are quoted.
What does it cost to paint a room?
Painting work is typically priced per square metre of wall and ceiling surface, often with a surcharge if filling or priming is needed first. The decisive figure is therefore not the room's floor area but the total surface area to be painted — and that is larger than most people think, because a room with a 2.5 m ceiling easily has twice as much wall area as floor area. Always ask for a price per square metre, not a flat price per room, if you want to compare quotes across several rooms of different sizes.
What does new flooring cost per square metre?
Flooring is usually priced per square metre for the material itself, plus a separate price for laying, and often a surcharge for waste — particularly with patterns like herringbone or diagonal laying, where offcuts cannot be reused. Once you have the measured floor area for each room, you can multiply directly: material price × area × waste factor, plus laying. Ask the supplier what waste percentage they allow for for the specific shape of your room — an out-of-square or irregular room typically has more waste than a regular one.
Does the cheapest quote always mean it is best?
No — and that is one of the most expensive mistakes to overlook in a budget built on numbers alone. Two quotes at the same price per square metre can cover very different scopes: is filling and priming included, or does it come as an extra charge along the way? Is time allowed for moving furniture and covering surfaces, or does the contractor assume the room is already empty? The cheapest figure on paper is often the figure with the most caveats hidden in the small print. Always ask for an itemised price that shows what is included and what is not — that way you can compare like with like, not just bottom lines.
How to put the budget together, room by room
- Measure each room separately — floor, wall and ceiling if relevant, with the areas each task requires.
- List every item you are considering per room: paint, flooring, tiling, electrical work, plumbing, joinery.
- Get a price per square metre for each item, either from your own quotes or from a professional.
- Multiply price by area for each room and each item, and add it all up to a total figure.
- Add a buffer on top. 10–20% is common in a renovation — more if there are hidden surprises to fear (damp, old installations, a wall that turns out not to be what you thought).
Items that should not be calculated per square metre
Not everything scales with area. A new kitchen, a new boiler, a staircase, or electrical work with a fixed number of sockets is often priced as a lump sum, regardless of the room's size. Do not mix that kind of item into a per-square-metre calculation — set it as a fixed sum per room or per task instead, so the budget does not become artificially precise on a figure that does not actually depend on area.
How long does a budget stay valid?
A budget built on quotes gathered today is not valid forever. Material prices change, contractors' calendars fill up, and a quote that was current three months ago can easily have shifted 10–15% by the time the work finally starts. Put a date on your budget, and ask for the prices to be reconfirmed if more than a couple of months pass between the budget being made and the work starting.
Why do budgets often get more expensive along the way?
Most renovation budgets grow, not because contractors cheat, but because a budget made before work starts is built on what could be seen. Damp damage behind an old floor, electrical installations that do not meet today's standards, or a wall that turns out to be in worse condition than assumed, are only discovered once work is under way. That is precisely why the 10–20% buffer belongs in the budget from the start — not as an afterthought, but as a fixed part of the calculation.
What HouseSense does
HouseSense builds the budget on top of the areas the app has itself measured in the takeoff: you set a price per square metre or per unit for each item, and the app multiplies it by the measured area for that specific room — not an estimated figure. Items can also be priced as a lump sum if they do not scale with area, for example a whole floor in one go. The feature assumes the room has been measured first; without measurements there is no area to multiply a price by.
How to use the budget from here
- Use it to compare quotes — but only quotes that cover the same items and caveats.
- Use it to plan the order of the work, once you can see which items weigh heaviest.
- Reconfirm the prices if several months pass before the work starts.
- Have a contractor see the room before the price is finally locked in — a budget is still an estimate until someone has stood in the room and confirmed it.