Quick answer: To calculate floor area in the UK, measure each floor between the inside faces of the external walls, multiply length by width in metres, and add the floors together. A two-storey house with an internal footprint of 5.70 m × 7.80 m has 44.46 m² per floor, or 88.92 m² (about 957 sq ft) in total.
Floor area is the single figure behind house prices per square foot, Energy Performance Certificates, extension plans and the space standards councils apply to new homes. This guide shows how to work it out for a whole home rather than a single room, what the official definitions include and leave out, and how to sanity-check a figure on an estate agent’s floor plan. It sits within the area and property measurement guides, which cover plots, rooms and land as well.
What does “floor area” actually mean in the UK?
In UK property, “floor area” usually means gross internal area (GIA): the floor space measured to the inside face of the external walls on every floor. The government’s Nationally Described Space Standard defines it as the total floor space between the internal faces of the perimeter walls, including partitions, structural elements, cupboards, ducts, flights of stairs and voids above stairs.
That is different from simply adding up the rooms. Room areas leave out the thickness of the internal walls, so they always total slightly less than the GIA. Surveyors also use a gross external area (measured to the outside of the walls) for some building and planning purposes, so it is worth checking which version a document is quoting before comparing two figures.
| Measure | Measured to | Where you will see it |
|---|---|---|
| Sum of room areas | The walls of each room | Flooring, carpet and paint estimates |
| Gross internal area (GIA) | Inside face of the external walls, on each floor | Space standards, many floor plans, valuations |
| Total useful floor area | Gross floor area, measured using RICS guidance | Energy Performance Certificates |
| Gross external area (GEA) | Outside face of the external walls | Some planning and building cost calculations |
What do you need to measure floor area?
- A tape measure or laser measure. An 8 m tape covers most UK rooms; a laser distance meter is faster for long runs and full floors.
- Squared paper or a sketching app to draw each floor as a simple plan.
- A calculator and somewhere to keep a running total.
- A second person for holding the tape on long walls, if possible.
Work in metres to two decimal places throughout. If the smaller markings on your tape are unfamiliar, the guide to reading a UK tape measure explains both scales.
How do you calculate the floor area of a house step by step?
Measure each floor as a set of rectangles, multiply length by width for each, then add every rectangle on every floor. The method is the same whether you want GIA or the sum of rooms; only the starting and finishing points of the tape change.
- Sketch each floor. Draw the outline of the ground floor, then each upper floor, marking rooms, the staircase and any projections such as bay windows.
- Choose your definition. For GIA, measure from the inside face of one external wall to the inside face of the opposite one, straight through internal doorways. For room areas, measure each room separately.
- Split awkward shapes into rectangles. An L-shaped floor becomes two rectangles; a rear extension becomes a separate rectangle added on.
- Measure at floor level. Skirting boards are thin enough to ignore. Keep the tape flat on the floor and move furniture aside if it pushes the tape off line.
- Multiply and record. Write each area on the sketch, rounded to two decimal places.
- Handle low ceilings. In lofts and rooms in the roof, mark where the headroom falls below 1.5 m and 0.9 m (see the loft section below).
- Add the floors together. Include the staircase on each floor it passes through; the space standard counts flights of stairs and the void above them.
What does a worked UK example look like?
A typical two-storey house with an internal footprint of 5.70 m × 7.80 m has a gross internal area of 88.92 m². The diagram above shows the ground floor. Measured wall to wall, it is 5.70 × 7.80 = 44.46 m². The first floor sits directly above with the same footprint, so it adds another 44.46 m².
| Area | Dimensions | Square metres | Square feet |
|---|---|---|---|
| Living room | 3.80 × 4.60 m | 17.48 m² | 188.2 sq ft |
| Hall (including stairs) | 1.80 × 4.60 m | 8.28 m² | 89.1 sq ft |
| Kitchen-diner | 5.70 × 3.10 m | 17.67 m² | 190.2 sq ft |
| Ground floor, rooms only | — | 43.43 m² | 467.5 sq ft |
| Ground floor GIA | 5.70 × 7.80 m | 44.46 m² | 478.6 sq ft |
| First floor GIA | 5.70 × 7.80 m | 44.46 m² | 478.6 sq ft |
| Whole house GIA | — | 88.92 m² | 957.1 sq ft |
For context, the Nationally Described Space Standard sets a minimum GIA of 93 m² for a new two-storey, three-bedroom home for five people. This example would fall a little short of that. The standard applies to new homes where a council has adopted it, not to existing houses.
How do you convert floor area from square metres to square feet?
Multiply square metres by 10.764 to get square feet, or multiply square feet by 0.0929 to get square metres. One square foot is exactly 0.09290304 m², because a foot is exactly 0.3048 m. UK estate agents often quote both, so converting lets you compare a listing with your own measurements. The site’s area converter handles other units, including acres and hectares.
Floor area: square metres to square feet
m²= sq ft| Square metres | Square feet | Square feet | Square metres |
|---|---|---|---|
| 20 m² | 215.3 sq ft | 500 sq ft | 46.5 m² |
| 50 m² | 538.2 sq ft | 750 sq ft | 69.7 m² |
| 70 m² | 753.5 sq ft | 1,000 sq ft | 92.9 m² |
| 93 m² | 1,001.0 sq ft | 1,250 sq ft | 116.1 m² |
| 100 m² | 1,076.4 sq ft | 1,500 sq ft | 139.4 m² |
| 150 m² | 1,614.6 sq ft | 2,000 sq ft | 185.8 m² |
How do you measure floor area in a loft or room with a sloping ceiling?
Under the Nationally Described Space Standard, floor with less than 1.5 m of headroom is left out of the GIA unless it is used only for storage. Storage space with 0.9 m to 1.5 m of headroom counts at 50% of its floor area, and anything lower than 0.9 m is not counted at all. Estate agents do not always follow this rule, which is one reason loft conversions can look larger on paper than they feel in use.
If the loft in the diagram is 5.0 m long, its total floor is 6.0 × 5.0 = 30 m². Only the central strip counts in full: 3.0 × 5.0 = 15 m². The two 0.6 m bands add 6 m² of floor, which counts as 3 m² if used solely for storage. The 9 m² under the lowest part of the roof is excluded, so the loft contributes 15 m² or 18 m² to the GIA, not 30 m².
How do you handle bay windows, alcoves and chimney breasts?
Add bays as an extra shape and subtract chimney breasts that project into the room. For GIA, a chimney breast inside the external walls is a structural element and stays in the figure; for a room-by-room total used to order flooring, you would take it out.
- Square bay: a rectangle. A bay 2.4 m wide projecting 0.6 m adds 1.44 m².
- Angled (canted) bay: a trapezium. Add the back and front widths, halve the result and multiply by the depth. A bay 2.4 m wide at the wall and 1.2 m at the front, projecting 0.6 m, adds (2.4 + 1.2) ÷ 2 × 0.6 = 1.08 m².
- Curved bay: treat a semicircle as π × radius² ÷ 2. A semicircular bay with a 0.9 m radius adds about 1.27 m².
- Alcoves: include them if you are measuring to the external walls; measure them separately if you are buying carpet.
What is included and excluded from floor area?
GIA includes internal walls, cupboards, stairs and built-in storage, but leaves out low-headroom areas and anything outside the external walls. The space standard also counts built-in wardrobes towards the total, though they must not reduce a bedroom’s width below its minimum.
| Usually counted in GIA | Usually left out or shown separately |
|---|---|
| Internal walls and partitions | External wall thickness |
| Staircases, on each floor they occupy | Floor with under 1.5 m headroom (unless storage) |
| Cupboards, ducts and built-in wardrobes | Balconies, terraces and gardens |
| Hallways and landings | Detached garages and outbuildings |
| Chimney breasts inside the walls | Open porches and car ports |
Integral garages and conservatories are handled differently from one document to another. Some floor plans include them in the headline figure and others list them separately, so read the small print before comparing two homes.
Where can you find the official floor area of a UK home?
The quickest source is the property’s Energy Performance Certificate, which lists a total floor area in square metres. You can look it up free on the government’s Find an energy certificate service for homes in England, Wales and Northern Ireland. The EPC regulations define total useful floor area as gross floor area measured in line with Royal Institution of Chartered Surveyors guidance.
Treat EPC figures and agents’ plans as a guide rather than a guarantee. Floor plans often carry a note saying they are approximate and not to scale, and an older EPC will not reflect a later extension. If a purchase price or a rent depends on the exact figure, ask a chartered surveyor to measure it.
What are the common mistakes when calculating floor area?
- Mixing units. Multiplying metres by centimetres, or feet by metres, gives a meaningless number. Convert everything to metres first.
- Squaring the conversion wrongly. There are 10.764 sq ft in a square metre, not 3.281. The length factor must be squared for area.
- Counting stairs twice or not at all. Under the space standard, the stair flight and the void above it are part of the GIA on each floor.
- Comparing GIA with a room total. The difference is internal walls, often a few square metres across a whole house.
- Counting the whole loft. Sloping ceilings can remove a large share of the usable floor, as the loft example shows.
- Measuring a diagonal. Keep the tape parallel to the walls. For stairwells and split-level rooms, the guide to measuring a staircase shows where to take readings.
Frequently asked questions
How do I work out the square footage of my house?
Measure each floor in metres between the inside faces of the external walls, multiply length by width, add the floors together and multiply the total by 10.764. A house with 88.92 m² of floor area is about 957 sq ft.
Does floor area include the stairs?
Yes, for gross internal area. The Nationally Described Space Standard includes flights of stairs and the voids above stairs, so the staircase counts on each floor it occupies.
Is floor area measured inside or outside the walls?
Most UK residential figures, including space standards and many floor plans, use gross internal area, measured to the inside face of the external walls. Gross external area, measured to the outside, is used for some planning and building cost purposes.
Does a loft room count as floor area?
Only the part with at least 1.5 m of headroom counts in full under the space standard. Storage areas with 0.9 m to 1.5 m of headroom count at half their area, and anything lower is excluded.
Where can I find my home’s floor area for free?
Look up the property on the government’s Find an energy certificate service. The Energy Performance Certificate shows a total floor area in square metres for homes in England, Wales and Northern Ireland.
Sources
- Technical housing standards: Nationally Described Space Standard (Ministry of Housing, Communities and Local Government, gov.uk)
- Find an energy certificate (gov.uk)
- Energy Performance of Buildings Certificates: glossary (gov.uk, PDF)
- Royal Institution of Chartered Surveyors (property measurement standards)