Bathroom renovation budget: how to measure up and work it out yourself

In short

A bathroom budget doesn't come from guesswork. It comes from measurements. Measure the floor, walls, internal corners and openings, and count every water, waste and electrical point. Then list the work trade by trade and keep labour separate from materials. Only with a list like that can you compare two bathroom quotes without comparing chalk with cheese.

Why work out your bathroom before you call anyone in

Because otherwise you're playing a game where only one player knows the rules. The tradesperson knows how many square metres of tiling they're looking at. You don't. Once you've measured the bathroom yourself, the whole conversation changes. You're no longer asking for a price, you're asking about specific items.

There's a practical upside too. Ordering materials gets easier, you'll spot straight away if someone has doubled the area, and you can decide where to save and where it's better not to. One more thing: tradespeople like working for people who know what they want. That's not a cliché, it saves time on both sides.

If you're wondering how to budget a bathroom renovation with no experience, the answer is simple. A tape measure, paper, a pencil and one quiet afternoon. If you got through maths at school, you'll manage this.

Before you start crunching numbers, check the paperwork side. Some bathroom work, such as new drainage, ventilation or electrical changes, may fall under building regulations, so it's worth asking your local council's building control team before you start. If you live in a flat, let the freeholder, managing agent or residents' association know, especially if anyone will be touching the soil stack or shared pipework, and check your lease for any rules on alterations.

What to measure in the bathroom

Measure twice. Old walls are rarely straight or square, so a wall can measure differently at the top than at the bottom. When you do the sums, use the larger figure.

Floor area

Length times width. If the bathroom has an alcove or is L-shaped, split it into rectangles and add the areas together. Measure the whole floor, including under the bath if it's coming out and being replaced. The floor area is what you'll use for floor tiles, levelling compound, primer and waterproofing.

Wall tiling area

The basic formula is simple: the room's perimeter times the tiling height, minus the door and window. The perimeter is the total length of all the walls. The tiling height is how high you want the tiles to go, not necessarily the ceiling height. Some people tile floor to ceiling, some up to door frame height, some only around the shower and basin.

Watch out for hidden areas. A boxed-in wall for a wall-hung WC frame, a tiled bath panel, a built-in shelf or a niche all add square metres you won't spot at first glance. Work them out separately and add them on.

Lengths of corners and edges

Corners are measured in linear metres. You need them for waterproofing tape, silicone and corner trims. Add up the vertical internal corners (tiling height times the number of corners), the joint between wall and floor (roughly the floor perimeter minus the door) and the perimeter of the bath or shower tray. Measure external corners, where tiles meet on an edge, separately. Those need trims or mitred edges.

Water, waste and electrical points

No measuring here, just counting. Every fitting has its own connections. The basin needs cold, hot and waste. The washing machine needs cold and waste. The WC needs cold and waste. The shower or bath needs hot, cold and waste. For electrics, count the sockets (where allowed), lights, switches, extractor fan, water heater and any electric heated towel rail.

Openings and penetrations

Door, window, air vent, access panel to the soil stack. Write down their sizes. You deduct openings from the tiling area, but window and door reveals add tiling. Small openings of up to about half a square metre usually aren't deducted, because they mean more work around them, not less.

DIY guide: how to measure a bathroom

1. Measure the length and width of the floor in two places and note the larger figure.
2. Work out the floor area, splitting an awkward layout into rectangles.
3. Measure all the walls, add them up to get the perimeter and multiply by the tiling height.
4. Deduct the door and window, add the reveals, the boxed-in WC wall and the bath panel.
5. Measure the vertical corners, the wall-to-floor joint and the bath perimeter in linear metres.
6. Count the water, waste and electrical points fitting by fitting.
7. Draw a simple sketch with dimensions and the position of each fitting.
8. Add the waste allowance to the wall and floor tile areas and round up to whole boxes.

The sketch doesn't need to be a work of art. It just has to show the tradesperson where the door is, where the soil stack is and where you want the basin. Take a photo of it and send it with photos of the bathroom. You'll save yourself one pointless site visit.

How to work out the waste allowance for tiles

Tiles get cut. Bits from the edges, around pipes and at corners end up in the skip. So never buy exactly what your measurements come to.

As a rough guide, for a standard tile size laid straight, the waste allowance is usually around ten per cent. For diagonal or herringbone layouts, or large-format tiles, it goes up, roughly to fifteen per cent and sometimes more. Large format means fewer grout lines, but every bad cut costs more and the offcuts are often no use for anything. A small bathroom with lots of corners, niches and pipes also pushes waste up, because a bigger share of the tiles has to be cut.

Your tiler will give you a more accurate figure once they see the tile size and layout. The manufacturer or retailer sometimes states a recommended allowance too. A few more rules:

• Round up to whole boxes, as they don't usually sell tiles loose.
• Buy from a single batch, as the shade can vary between batches.
• Keep a few tiles back for future repairs. In ten years' time you won't find the same ones.
• Count decorative tiles and border strips by the piece or linear metre, not by area.

If you'd like to know more about what the tiling itself involves, have a look at tiling work and its individual items.

List of items trade by trade

A bathroom renovation isn't one job. It's several trades taking turns in a set order. Once you list them, you'll see where the price is made up. How the work runs over time is covered in the article on a bathroom renovation week by week.

Strip-out and demolition

Removing the sanitaryware, hacking off wall and floor tiles, possibly taking out an old panelled bathroom pod, carrying out and taking away the rubble. You'll find the scope and units under demolition work. Rubble is priced by volume or number of skips, not by mood.

Plumbing and waste

New hot and cold supply pipes, waste pipes, connections for fittings, valves, connection to the stack and a pressure test. The items are set out nicely under plumbing work. If there's a gas boiler or water heater in the bathroom, only a Gas Safe registered engineer may touch the gas.

Electrics

New wiring, sockets where permitted, lights, extractor fan, supply for the water heater, and testing and certification. Electrical work must be done by a qualified, registered electrician, and bathrooms come with extra safety rules. You'll find the breakdown under electrical work.

Building and plastering work

Straightening walls, plastering, a plasterboard stud wall for the WC frame, filling in chases, floor levelling compound and, if needed, adjusting the door opening.

Waterproofing

Primer, tanking coat, tape for corners and seals around pipe penetrations. It's priced by the area and linear metres you've already measured. You'll find the item as waterproofing around the bath, basin and under the shower.

Wall and floor tiling

Laying wall and floor tiles, grouting, trims, cuts and mitred edges, siliconing the corners.

Sanitaryware and accessories

Fitting the basin, WC, bath or shower, taps, mirror, vanity unit, holders, hooks and towel rail. Each piece is priced separately, so it pays to have an exact list counted down to the last item.

Labour, sundries and main materials

This is where quotes most often get muddled. Three things get mixed together, and you need to see them separately.

• Labour is what the tradesperson does with their own hands and tools. Laying, fitting, stripping out.
• Sundries are everything that disappears into the wall or under the tiles. Adhesive, grout, primer, waterproofing, tape, silicone, plasterboard, studs, pipes, cables, back boxes.
• Main materials are the things you choose. Wall and floor tiles, basin, WC, bath, shower screen, taps, lights.

Customers often buy the main materials themselves to keep control of both the look and the cost. The tradesperson usually supplies the sundries, because they know which adhesive and waterproofing they need. Agree this in writing. If you don't, the classic happens: each of you thinks the other one is buying the adhesive.

Ask for every item on the quote to state clearly whether it includes materials or labour only. The same item with and without materials gives two completely different figures.

What's often missing from quotes

A quote can look cheap until you notice what isn't in it. Go through this list and tick off each item you can see on the quote:

• rubble removal and disposal, including the skip,
• access panels to the stack and valves,
• pressure test of the water pipes,
• electrical installation certificate,
• extractor fan and its wiring,
• siliconing the corners and around the sanitaryware,
• corner trims and tile edge trims,
• adjusting or trimming the door after the floor level rises,
• levelling walls and floor before tiling,
• delivery of materials and carrying them upstairs,
• cleaning up after the work.

None of this is exotic. Almost every bathroom needs it. If it's not on the quote, either the tradesperson forgot or it'll turn up later as an "extra". Ask before you sign. For other details such as ventilation or silicone, you'll find the background on the page about bathroom renovation costs including labour and materials.

How to compare two bathroom quotes

Two quotes, two figures, one looks better. But it's the contents you need to compare, not the bottom line.

Same quantities

Check how many square metres of tiling each one has allowed for. If they're wildly different, one of them probably measured by eye. Your own measurements are the referee here.

Same scope

Do both include the strip-out? The boxed-in WC wall? New pipework, or just connecting to the old? Sometimes the cheaper quote simply includes less work.

Units

Square metres, linear metres, pieces, complete sets. Be wary of items marked "complete" or "fixed price". They're not bad in themselves, but you want to know exactly what's in them. "Electrics complete" could mean three light fittings or a full rewire with certification.

Day rate or itemised

A day or hourly rate is fair for small, unpredictable jobs. For a whole bathroom, though, it's hard to compare, because you don't know how many hours it'll end up taking. An itemised quote gives you a clear framework. If you get one quote on an hourly rate and another itemised, ask the first for at least an estimate of the hours for each stage.

How to avoid getting burnt when choosing the whole firm, not just the price, is covered in 9 essential tips for hiring the right contractor.

A contingency for surprises in older homes

An old bathroom is like a parcel from an unknown sender. Until you open it, you've no idea what's inside.

Once the tiles come off, you might find the plaster is only staying up out of habit. That there's a void under the floor tiles. That the old steel pipes are furred up, or that the soil stack looks worse than you'd hoped. The wiring might be decades old and without a proper earth. The floor might not be level, not even roughly.

The tradesperson can't see any of this on a site visit, because they don't have X-ray vision. So keep a contingency in your budget that isn't earmarked for anything. The older the property and the less you know about previous work, the bigger it should be. If you don't use it, you can treat yourself to nicer taps. If you do, you won't be scrabbling around halfway through for money for new pipes.

Agree with the tradesperson how surprises like these will be handled. Ideally, they show you, take photos and tell you what it'll cost extra before carrying on.

How to work out your bathroom budget in NUMIQ

Once you have your measurements, the rest is just putting it together. In NUMIQ you pick items from the building works price list, such as hacking off tiles, laying floor tiles, a water point or fitting a WC. For each one you enter the quantity you've measured. That gives you an itemised budget showing labour, materials and totals by trade.

A budget like this does two jobs. First, as a guide to roughly what to expect. Then as a template for comparing quotes, because you've got the same items and the same quantities and can drop in the tradespeople's figures next to them. And it helps a tradesperson put together a clear quote without scribbling it on the back of an envelope.

If you'd first like to see the usual price range for bathrooms and what drives it, have a look at the bathroom renovation page in the NUMIQ price list. Then work out your own in the app, with your measurements and your fittings.