How to work out price per square metre and compare flats

Two flats can both be listed at the same price and be wildly different homes. One might be a squeezed one bed with a bedroom you can barely fit a double bed into. The other might be a generous one bed with room for a proper desk and a sofa that isn't a compromise.

Price per square metre cuts through that. It tells you what you're paying for each unit of floor space, so you can line up flats of different sizes on something closer to equal terms. It won't give you the whole story, and I'll be honest about where it falls over later. But as a first filter it's one of the most useful numbers a buyer can work out, and almost nobody on the viewing circuit bothers.

You've got two main sources, and it's worth checking both.

The first is the Energy Performance Certificate. Every property being sold needs one, and it states a total floor area in square metres. You can search for it for free on the government's EPC register using the address or postcode. Agents sometimes quote the figure in the listing, but if they don't, you can look it up yourself in a couple of minutes.

The second is the floorplan in the listing. Some show a total area, often in both square feet and square metres. Others only show room dimensions, in which case you'd have to multiply and add them up yourself, which gets fiddly fast. Where a total is given, note whether it's marked as approximate. It nearly always is.

If the two figures disagree, don't panic. Don't ignore it either. Ask the agent which they trust and why. A gap might come from different measuring methods, or from a conversion or extension that happened after the EPC was done.

It's just division. Take the asking price and divide it by the floor area in square metres.

So if a flat were listed at 300,000 pounds and measured 50 square metres, you'd divide 300,000 by 50 and get 6,000 pounds per square metre. That's a made up example to show the method, not a figure for any real area.

If a floorplan only gives square feet, convert first. One square metre is roughly 10.76 square feet, so divide the square feet by 10.76 to get square metres. Do it the same way for every flat on your list, or the comparison is worthless.

A spreadsheet helps once you've got more than three or four flats in play. Put in the address, asking price, floor area, source of the area, and the result. Add a column for the lease length if they're leasehold, because that matters more than people expect.

The number only means something if you compare flats that are genuinely similar. Stick to the same neighbourhood, a similar type of building, and a similar condition. Comparing a new build penthouse by the river with a tired ex council flat two streets back tells you nothing useful.

Also look at what the asking price is based on. If you're checking against sold prices, the Land Registry's price paid data shows what flats actually went for. Pair those sales with each flat's EPC floor area and you can see what buyers really paid per square metre locally, rather than what sellers hoped for.

Once you've got a handful of comparable figures, you'll see a range. A flat sitting well above it needs a reason, like a stunning refurbishment or a long lease. One sitting well below it deserves a harder look too. Cheap per square metre sometimes just means cheap for a reason.

Here's the honest bit. Price per square metre is a tool, not a verdict.

First, layout. Fifty square metres of sensible, usable space beats fifty with a long dead corridor and awkward corners. The figure can't see that, but you can when you stand in the flat.

Second, what's counted. Floor area measurements can include things like stairwells, thick walls or odd sloping ceiling areas, depending on who measured and how. EPC areas are assessed on a standard basis, but they can still contain errors.

Third, the lease. A flat with a short lease, high service charge or heavy ground rent can look cheap per square metre and still be an expensive mistake. If lease length is under 80 years, extending can involve marriage value, which can push the cost up sharply. Ask a solicitor to check the lease before you rely on any comparison.

Fourth, everything the maths ignores. Light, noise, outlook, parking, balcony, floor level, building condition and the neighbours all affect value. Buyers pay extra for a quiet flat with a view, and rightly so.

Use the number to shortlist and to negotiate. Don't use it to decide on its own.

Once you've found a flat you like, put its price per square metre next to two or three comparable sales nearby. If it's noticeably higher, you've got a calm, factual basis for a lower offer. Agents hear plenty of emotional haggling. A tidy comparison is harder to wave away.

If the EPC area is smaller than the listing suggests, mention it politely and ask for an explanation. A sensible agent will give you one.

And remember a surveyor's valuation is what your lender cares about. Your own figures help you decide what to offer, but the valuer may see things differently. Treat price per square metre as one honest voice in the room, not the only one.