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Why does the listing show a different floor area than the official record?

Because a listing often adds areas together differently than the public property record does — and because the registered figure can simply be out of date. Here are the five explanations, in the order you should check them.

A listing usually pulls its figure from the record

The floor area in a property listing usually comes from the public property record. That's the registered baseline, and it's also what the price-per-square-metre in the advert is calculated on. Discrepancies aren't therefore normal — but they aren't necessarily suspicious either. Almost every one of them has a concrete explanation you can simply ask for.

The five explanations below are sorted by how often they turn out to be the answer. Check them in this order and you'll spend the least time getting there.

1. The listing adds several fields together

This is by far the most common reason a listing and the record show different figures. The property record has separate fields for living area, basement area, converted attic, sunroom, garage and carport. A listing that says "1,700 sq ft" may have added the 1,300 sq ft living area to the 400 sq ft basement.

That isn't wrong in itself — a finished basement is floor space you can actually use. But it's a different figure from the one you're comparing against when you look at price-per-square-metre in the neighbourhood, because those are calculated on living area alone.

How to check it: add the record's fields together one at a time, and see which combination hits the listing's number. If living area plus basement lands exactly on it, you've found your answer in thirty seconds.

2. The record hasn't been updated

If there's been an extension, a converted garage, a finished attic or an enclosed porch — and it was never reported — the old figure is still what's on file. The seller and the agent know the house as it looks today, and the listing describes that reality. The record describes whatever was last reported.

That's a warning light, not necessarily a problem. But it's worth asking: have there been changes that aren't registered, and was a permit ever obtained? An unregistered area can mean an approval is missing, and that bill follows the house to the next owner.

3. A new survey has been carried out

Sometimes the seller has had a licensed surveyor measure the home because the registered figure was wrong. In that case the listing may carry the new, measured figure while the record hasn't been corrected yet — a correction takes time to process.

This is the best of the five explanations, because there's professional evidence behind it. Ask to see the survey. If a surveyor's report exists, the figure is documented, and the matter is closed.

4. Two different fields are being compared

Living area, footprint and total building area are three different things, and each sits in its own place on the record.

Footprint is the house's outline on the plot. A house with 1,700 sq ft of total building area spread over two equal storeys therefore has a footprint of roughly 850 sq ft. Compare a living area against a footprint on a house like that, and it looks as though 850 sq ft is missing — when nothing is missing at all.

Read the field names, not just the numbers. It's the same mistake people make when they measure their own house and get a fright.

5. The listing quotes an internal measurement

The registered area is usually measured externally — to the outside of the exterior walls, with internal partitions counted in. An internal, wall-to-wall measurement is typically 10–20% smaller, and the gap is largest in a small home with thick walls.

So if you see an area in the listing that's lower than the registered figure, and the difference roughly matches the walls, it's probably a net area that's crept in — typically taken from a floor plan where the individual rooms' areas have been added up.

Do the rule-of-thumb maths: the exterior walls take up roughly the wall thickness times the house's perimeter. A house measuring 8 × 12 m has a perimeter of 2 × (8 + 12) = 40 m; with 35 cm exterior walls that's 40 × 0.35 = 14 m² (about 150 sq ft). The rule runs slightly high, because the corners get counted twice, so the true figure is closer to 13 m² — and internal partitions typically add another 2–4 m² on top. On a 96 m² exterior footprint that's around 17%. If the difference matches that, there's no disagreement about the house — only about the way it's measured.

As a buyer: how to get a handle on it at a viewing

You don't need to be an expert. You just need to be systematic:

• Pull up the property's record before you go, and write down the individual fields.
• Measure two or three rooms with a tape measure — the biggest ones. Not to check the whole house, but to see whether the order of magnitude holds up.
• Measure the exterior wall thickness at a window reveal, from the inner face to the outer face. Without that figure you can't translate between internal and external.
• Ask the agent directly: "Which fields make up that 1,700 sq ft?" It's a completely normal question, and the answer should be easy to follow.
• Ask for it in writing if anything doesn't add up. Verbal explanations at a viewing don't survive to completion day.

HouseSense is built for exactly that situation: scan the home with your iPhone's LiDAR in the few minutes you have at a viewing, or draw it after the visit on graph paper with your finger. You get a measured floor plan with area per room and in total — internal, wall to wall. It isn't a registered figure, and it isn't meant to be. It's your own, measured number to hold the listing up against.

As a seller: make sure the numbers can be explained

You don't need a single figure. You need to be able to account for where each figure comes from. "1,300 sq ft living area per the record plus 400 sq ft finished basement" is information a buyer can weigh up. "1,700 sq ft" with no explanation is information a buyer can get angry about later.

If you know the record doesn't match the house, contact the relevant authority well before the sale — the exact office depends on where you are, but it's usually the same body that issued the original record. A correction takes time, and it's far better to have it sorted before the listing goes live than to discover it when the buyer turns up with a tape measure of their own.

When is the difference too big to ignore?

Work out the walls — wall thickness times perimeter, plus 2–4 m² for partitions — and add up the other fields in the record. If those two things together explain the gap, everything is as it should be.

If 10–20 m² is left over that neither the walls nor the other fields can explain, something is either unregistered or wrongly registered. At that point it isn't a maths error, it's a question of what's actually approved on the property. That question should go to the agent, and ultimately to the authority that keeps the record — and it should be asked before you sign anything.