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What's the difference between living area, gross area and net area?

Gross area is measured around the outside of the exterior walls, living area is the inhabited part of that, and net area is the actual floor inside the rooms. Here are all three worked out for the same house.

The three figures, in short

All three area terms describe the same house, but they put the tape measure in different places. That's why it's entirely normal for a house to be "80 m²" in the listing and 66 m² on the floor — without anyone having cheated.

• Gross area (also called gross floor area): measured from the outer face of the exterior wall to the outer face of the exterior wall. Every wall counts — exterior walls and partition walls alike. One figure per storey, added together.
• Living area: the gross area minus the parts that aren't living space — an integrated garage, carport, unheated outbuilding, and in apartment blocks typically also stairwells and shared basement rooms. It's the figure the public building register usually states for a home.
• Net area: the sum of the individual rooms' floor areas, measured internally from wall to wall. No walls count. It's the figure you can check yourself with a tape measure.

The order is always the same: gross area ≥ living area ≥ net area. If your sums put the net area as the biggest of the three, there's an error somewhere.

The worked example: an 80 m² house

Take a simple, rectangular single-storey house. On the outside it measures 10.00 m × 8.00 m. The exterior wall is an ordinary cavity wall: 11 cm brick outside, 13 cm insulation, 11 cm brick inside — 35 cm in total. The internal partition walls are lightweight, 10 cm thick.

1. The gross area

Gross area is the outside dimensions multiplied together:

10.00 m × 8.00 m = 80.00 m²

That's the figure in the listing, and it describes the house's footprint on the plot. Note that nothing has been deducted: the 80 m² includes both the exterior walls and the partition walls.

2. What the exterior walls eat up

The 35 cm exterior wall takes up space at both ends of both directions. So the internal dimensions become:

• Length: 10.00 − 0.35 − 0.35 = 9.30 m
• Width: 8.00 − 0.35 − 0.35 = 7.30 m
• Internal area inside the exterior walls: 9.30 × 7.30 = 67.89 m²

The exterior walls alone have eaten 80.00 − 67.89 = 12.11 m². That's 15% of the house — more than most people expect. The smaller the house, the harder this hits: a 60 m² house has almost as many running metres of exterior wall as an 80 m² one, but fewer square metres to spread them over.

3. The partition walls and the net area

Inside the house are three 10 cm partition walls, splitting the 9.30 × 7.30 m into four rooms:

• Living room: 4.50 × 7.30 = 32.85 m²
• Kitchen: 4.70 × 3.00 = 14.10 m²
• Bedroom: 2.40 × 4.20 = 10.08 m²
• Bathroom and hall: 2.20 × 4.20 = 9.24 m²

The net area is the sum: 32.85 + 14.10 + 10.08 + 9.24 = 66.27 m².

The maths adds up. The three partition walls together take up 0.10 × 7.30 + 0.10 × 4.70 + 0.10 × 4.20 = 1.62 m², and 67.89 − 1.62 = 66.27 m². No square metres have vanished — they're standing in the walls.

The final tally for the house

• Gross area: 80.00 m²
• Living area: 80.00 m² (the house has no garage or unheated outbuilding, so the two figures match here)
• Net area: 66.27 m²
• Total walls: 13.73 m² — or 17% of the gross area

If the house had also had a 15 m² integrated garage under the same roof, on top of the 80 m², the gross area would be 95 m² while the living area stayed at 80 m². That's exactly the kind of difference that makes two entirely correct figures about the same house look like a mistake.

Why does the sum of the rooms end up smaller than the house's area?

Because the walls have to stand somewhere. When someone adds up the rooms from a floor plan and wonders why 10-15 m² seem to be missing compared with the official area, the answer is almost always the same: the official area is measured around the outside of the house, and the rooms are measured inside the house's walls. There's no hidden room and no registration error involved.

Two things decide how big the gap turns out to be:

• The exterior wall's thickness. A newer low-energy house can have a 40-45 cm exterior wall against an older house's 30 cm. The new house is better insulated and has less floor for the same outside dimensions.
• The number of partition walls. Five small rooms cost more square metres in walls than one big room of the same total size.

Internal measurements are the only yardstick you can check yourself

What matters about the net area isn't that it's "more correct" than the gross area — it's that it's verifiable. You can walk into the living room with a tape measure, measure wall to wall, multiply, and get the same figure. You can't measure the gross area without standing outside and measuring across the plinth, the brickwork and any projections, and the living area requires you to know the rules for what can be deducted.

That's why HouseSense works in internal measurements. When you scan the home with the iPhone's LiDAR or draw it yourself on screen, it's the room's internal measurement the app shows and calculates from — the figure you can check with a tape measure if you're ever in doubt. If you want the gross area, you add the exterior wall's thickness on top; that's a decision, not a guess.

Two rooms must never count the same square metres

When two rooms share a wall, half of that wall sits "in" each room. Measure both rooms out to the wall's centre line and you count the wall twice, and the total comes out too big. Measure both rooms to the wall's surface and the wall counts zero times — which is the correct approach for net area, precisely because you can't walk on a wall.

That's also why a shared wall has to be one wall in the drawing, not two walls sitting on top of each other. Two walls stacked on top of each other give you a house that's 10 cm wider than it really is — and a drawing that's lying to you. In HouseSense, walls snap together into a single shared wall, precisely so that error can't happen.

The other area terms you might come across

• Heated area: the part of the living area with a radiator or underfloor heating. Used when calculating a home's energy consumption. An unheated conservatory doesn't count here.
• Registered area: the area as it's listed in the public building register. It can lag behind a renovation that was never reported.
• Basement area: as a rule stated separately, and not added on top of the living area unless the basement is approved for habitation.
• Area under a sloped ceiling: under a knee wall there are special measuring rules, and they differ from country to country — floor with very low headroom rarely counts in full. If you want to know how your own building is assessed, look it up in your country's public building register.

Which figure should you use for what?

• Buying a home? Compare using living area — it's the figure listings use, and the only one that's comparable across different houses. But walk in and get a feel for the net area too: two houses both listed at 110 m² living area can be very different to actually live in.
• Buying flooring, paint or underfloor heating? Use the net area, room by room. Materials go on floors and walls — not on gross areas.
• Getting the building approved by the authorities? As a rule, that's calculated on the gross area — and the authorities have the final say on how it's assessed. Use your own figures as preparation, not as the final answer.
• Getting a contractor's quote? Give the contractor the room's internal measurements and a floor and wall area per room. Nobody can price a single combined house area.