How To Check Floor Area On A Property In Japan

Two different ways to measure the same room

Japan's Ordinance on Real Property Registration (不動産登記規則), Article 115, sets the rule for how a building's registered floor area is calculated. The general rule measures, floor by floor, the horizontal projected area enclosed by the center line of the walls or pillars — the hekishin (壁芯) method. For a unit in a condominium or other sectioned building (区分建物), the rule is different: the registered floor area is instead measured by the inner surface line of the walls — the uchinori (内法) method, which covers only the exclusive-use section (専有部分) and excludes the hallway, stairwell, and other shared areas outright.

A detached house is not a 区分建物, so the general center-line rule applies to it — the same convention architects and builders use for a building-confirmation application under the Building Standards Act (建築基準法). That is why a house's registered floor area usually lines up closely with the figure used at the design stage. A condo unit is the exception: it is registered by the smaller, inner-surface method even though sales brochures and floor plans conventionally advertise the larger, wall-center figure.

Why a condo's registered number reads smaller than the brochure

Because a wall has thickness, measuring from its inner surface instead of its center line removes roughly half that thickness from every wall bordering the unit. The result is consistent and well documented in Japanese real estate practice: the exclusive floor area printed on a condo's registration record (登記簿面積, sometimes called 内法面積) is smaller than the exclusive floor area advertised in the pamphlet or floor plan (壁芯面積). This is not a discrepancy to chase down as an error — it is two different, both-correct measurements of the same unit, and the gap is larger for units with thicker interior or exterior walls.

Why the number on the registry, not the brochure, is what actually counts

The gap matters because Japan's mortgage tax credit (住宅ローン控除, formally 住宅借入金等特別控除) has a minimum floor area requirement, and the National Tax Agency judges that requirement against the floor area shown on the registration certificate (登記事項証明書) — not the marketing figure. For a condo, that means only the registered, inner-surface area of the exclusive-use section counts. The standard threshold has been 50 square meters, with a reduced 40-square-meter threshold available in some tax years for qualifying housing under an income cap — but both the threshold and the qualifying conditions have changed from year to year, so confirm the figures that apply to your purchase year directly with the NTA or a tax professional rather than relying on a fixed number. A unit advertised as "just over 50㎡" on a wall-center basis is exactly the kind of listing worth double-checking against the registered figure before assuming a size-based benefit applies.

When the building itself is bigger than what's on file

A separate issue, unrelated to measurement method, is a registered floor area that is simply out of date. The Real Property Registration Act (不動産登記法), Article 51, actually requires the owner to file a change registration (建物表題部変更登記) within one month of an addition, conversion, or other change to the registered floor area, and skipping it can technically draw a fine of up to ¥100,000. In practice this filing requirement is loosely enforced and easy to miss, so the registry commonly keeps showing the old, smaller number for years after a room was added, a veranda enclosed, a garage converted, or an attic finished. This is common on older houses and akiya that have been altered informally over the years. It is a different problem from the wall-center/inner-surface gap above, closer to the unregistered-building issue covered in How To Check If A Japanese Property Has An Unregistered Building — worth checking separately, especially if what you see on a viewing looks larger than what the registration record states.

Here is a practical way to check floor area before you commit to a property in Japan:

1. Order the building registration record and read the 表題部 (property description) floor area directly, rather than relying on the number in the listing. For a multi-story building it is printed per floor (for example, 1st floor and 2nd floor separately) rather than as a single combined total, so add the floors yourself if you need the whole building's area.
2. For a condo, expect the registered figure to be smaller than the brochure figure, and confirm which convention the marketing number uses. Ask the agent whether the advertised area is wall-center (壁芯); if so, the registered, inner-surface (内法) number on the record will normally read smaller — that gap alone is not a red flag.
3. If a size threshold matters — the mortgage tax credit or any other floor-area-based benefit — confirm eligibility against the registered figure before you rely on the marketing materials. Do this early enough to affect your financing plan, not after the loan application is in progress.
4. For a house, compare what you see on a viewing against the registered floor area, especially on older properties. A converted garage, an enclosed veranda, or an added room that looks lived-in but is not reflected in the 表題部 figure may mean a change registration was never filed.
5. If the transaction is size-sensitive — a per-square-meter price, or a renovation budget based on floor area — and you are not confident in the registered figure, commission a professional remeasurement from an architect, surveyor, or building inspector. Japan Property Research retrieves the registered figure as filed; it does not carry out a physical remeasurement.
6. Bring in a land and house investigator (土地家屋調査士) if a size discrepancy is large enough to affect the price, the loan amount, or a size-based tax benefit you are counting on. Building measurements and 表題部 description changes — including the floor area figure itself — are their specialty, not a judicial scrivener's (who handles ownership and mortgage registrations instead).

The most common mistake is assuming a condo's registered floor area and its advertised floor area should match, and treating the smaller registered number as a mistake to dispute. The second most common is assuming a house's visible floor space always matches what was filed with the registry, on a property that was quietly extended at some point without an update.

What you need to provide is the property address (and, for a condo, the specific room number).

• Building registration record: ¥1,500, states the registered floor area (床面積) for each floor, along with the building type and structure. For a multi-story building this is printed floor by floor, not as a single combined total — add the figures yourself if you need the whole-building area.
• Land registration record: ¥1,500, if you also need the registered land area for a house — see How To Check Land Boundaries In Japan for how that figure can differ from the real, on-the-ground area for a similar, though separate, reason.

A few honest caveats. Japan Property Research retrieves the floor area exactly as filed at the Legal Affairs Bureau; it does not commission a remeasurement or verify a listing's marketing figure against reality. A condo's registered number reading smaller than the brochure is normal and expected, not something we can "correct." And if a house has been informally extended without a change registration, the registry will keep showing the old figure until an owner files one — our due diligence checklist covers where a floor area check fits alongside the rest of a property review.

FAQ

Why is my condo's registered floor area smaller than the brochure or floor plan? Condo units are registered using the inner-surface (内法, uchinori) measurement method, which excludes the wall thickness, while marketing materials conventionally use the larger wall-center (壁芯, hekishin) method. The gap is a normal result of two valid, different measurement conventions — not an error to dispute.

Does floor area on the registration record affect my mortgage? It can. Japan's mortgage tax credit (住宅ローン控除) requires the floor area shown on the registration certificate to meet a minimum threshold, historically 50 square meters with a reduced 40-square-meter option in some tax years under an income cap. Confirm the current-year threshold and qualifying conditions with the National Tax Agency or a tax professional before assuming a property qualifies.

Is a house's registered floor area measured the same way as a condo's? No. A detached house is registered using the wall-center (壁芯) method, the same convention used for its building-confirmation drawings, so there is normally no measurement-method gap. A condo unit is registered using the inner-surface (内法) method instead, which is what creates its gap against marketing figures.

Can the registered floor area simply be wrong or out of date? Yes, in the sense that it can be out of date rather than incorrect for what was filed. An addition, conversion, or renovation that changed the building's floor area but was never reported through a change registration (建物表題部変更登記) will not appear on the record, even though it physically exists.

Can foreigners order a Japanese building's registration record? Yes. It is a public document with no nationality or residency requirement to request one.

Related guides:

• What Is Touki In Japan
• How To Read A Japanese Property Registration Record
• How To Check If A Japanese Property Has An Unregistered Building
• How To Check Land Boundaries In Japan
• How To Check Condo Ownership In Japan
• Japan Property Due Diligence Checklist
• How To Order A Japan Property Registration Record In English

• Ordinance on Real Property Registration (不動産登記規則), Article 115 — how a building's registered floor area is calculated, including the inner-surface rule for sectioned (condo) units — Japan e-Gov Law Search, Ministry of Justice
• 床面積の判定 (Determining floor area for the mortgage tax credit) — floor area is judged by the figure shown on the registration certificate (登記事項証明書), and for a condo unit only the exclusive-use portion counts — National Tax Agency, legal interpretation FAQ
• No.1211-3 中古住宅を取得し、令和４年以降に居住の用に供した場合（住宅借入金等特別控除）— mortgage tax credit floor area requirement for existing (used) housing — National Tax Agency, Tax Answer
• 専有面積の広告表示とは — the industry convention of advertising a condo's exclusive area using the wall-center (壁芯) method, distinct from the registered inner-surface (内法) figure — Sumitomo Mitsui Trust Real Estate, real estate glossary
• Real Property Registration Act (不動産登記法), Article 51 — the one-month deadline to file a change-of-description registration after registered matters such as floor area change, and the fine of up to ¥100,000 for failing to do so — Japan e-Gov Law Search, Ministry of Justice

A note on scope: the Article 115 measurement rule, the Article 51 change-registration deadline, and the mortgage tax credit's registration-based floor area test are matters of statute and National Tax Agency guidance, and apply nationwide. The specific floor area threshold and any reduced-threshold exception for the mortgage tax credit have changed across tax years — always confirm the figures current to your purchase year with the National Tax Agency or a tax professional rather than relying on a fixed number. For a significant, transaction-affecting size discrepancy, confirm the path forward with a land and house investigator (土地家屋調査士) — building measurements and description registrations are their area, not a judicial scrivener's.