Convert kg CO₂e per m² to per ft²
| kg CO₂e/m² | kg CO₂e/ft² |
|---|---|
| 0.5 | 0.04645 |
| 1 | 0.0929 |
| 1.5 | 0.1394 |
| 2 | 0.1858 |
| 3 | 0.2787 |
| 5 | 0.4645 |
| 10 | 0.929 |
| 20 | 1.858 |
| 50 | 4.645 |
| 100 | 9.29 |
Each row uses the same factor as the converter above: 1 kg CO₂e/m² = 0.0929 kg CO₂e/ft².
A building at 500 kg CO₂e/m² is 46.45 kg CO₂e/ft². Embodied carbon benchmarks are published per square metre in Europe and per square foot in the United States, so anyone reading a RIBA or LETI target against an American case study crosses this line. The conversion is exact — but it is also the smaller of the two problems, and the page says so.
To convert a carbon intensity from per square metre to per square foot, multiply by 0.09290304. So 500 kg CO₂e/m² is 46.45 kg CO₂e/ft². To go the other way, multiply by 10.7639 — 1 kg CO₂e/ft² is 10.76 kg CO₂e/m².
kg CO₂e/ft² = kg CO₂e/m² × 0.09290304. Reverse: × 10.7639. Exact by definition — the international foot is 0.3048 m, so a square foot is 0.3048² = 0.09290304 m² with nothing rounded. A square foot is the smaller area, so it carries the smaller share of the carbon.
| kg CO₂e/m² | kg CO₂e/ft² | Typical of |
|---|---|---|
| 300 | 27.9 | Ambitious low-carbon target |
| 500 | 46.5 | Good practice, new build |
| 800 | 74.3 | Typical commercial office |
| 1,200 | 111.5 | Carbon-intensive structure |
How to convert the intensity
Multiply by 0.0929 going to square feet, or by 10.764 coming back. The direction follows the rule that governs every intensity conversion: the number follows the size of the unit underneath it. A square foot is about a tenth of a square metre, so the carbon attributed to each one is about a tenth as much.
The reverse identity is the one worth memorising — 1 kg/ft² is 10.76 kg/m² — because American figures are usually the ones needing translation into a European benchmark rather than the other way round.
The unit is the easy part. The floor area is not.
Converting m² to ft² is exact. Deciding what floor area the intensity is measured over is not, and the spread between the common definitions is far larger than any unit conversion:
| Definition | Includes | Used in |
|---|---|---|
| Gross Internal Area (GIA) | Everything inside the external walls | UK benchmarks, RICS |
| Net Internal / lettable | Excludes cores, plant, circulation | Commercial leasing |
| Gross External Area | Measured to the outside face | Some cost planning |
| Gross Floor Area (US) | Broadly comparable to GIA, but defined separately | US practice, LEED |
Net internal area can be twenty per cent or more below gross internal on a building with substantial cores and plant — which means the same building can report two intensities differing by a quarter without either being wrong. Always state the area basis alongside the figure. A benchmark comparison that converts the units carefully and ignores the denominator has controlled the small error and left the large one.
And which life-cycle stages
The second thing a bare intensity does not tell you is what it covers. An embodied carbon figure may be:
- A1–A3 only — product stage, cradle to gate. The narrowest and most commonly quoted.
- A1–A5 — adding transport and construction.
- Upfront carbon — A1–A5, the basis most targets are set on.
- Whole life — including use-stage replacement (B) and end of life (C), per EN 15978.
Whole-life figures run substantially above upfront ones, so a comparison across boundaries is meaningless regardless of units. The RICS methodology sets out the convention; the EN 15978 whole-building calculator works to it.
To get a total from an intensity you multiply by area — and to get the intensity in the first place you need a material take-off. For that, the embodied carbon calculators by element: concrete and cement, steel and aluminium, timber and bio-materials, and the building envelope.
Frequently Asked Questions
Multiply by 0.09290304. So 500 kg CO₂e/m² is 46.45 kg CO₂e/ft². To reverse it, multiply by 10.7639 — one kg per square foot is 10.76 kg per square metre.
Because a square foot is about a tenth of a square metre, so the carbon attributed to each one is about a tenth as much. The number always follows the size of the unit underneath it — the same rule that governs every intensity conversion.
Yes. The international foot has been defined as exactly 0.3048 metres since 1959, so a square foot is exactly 0.3048 squared. There is no measurement uncertainty in the conversion at all — which cannot be said for the figures being converted.
Broadly, ambitious targets sit around 300 kg CO₂e/m² of upfront carbon, good practice new build nearer 500, and typical commercial offices higher again. But any such figure is meaningless without knowing which floor area it is divided by and which life-cycle stages it covers, both of which move the answer more than the unit does.
Whichever your benchmark specifies, and say which you used. UK practice generally uses gross internal area. Net internal or lettable area can be a fifth smaller on a building with substantial cores and plant, so the same building can report intensities differing by a quarter depending only on the denominator.
Usually because of boundary rather than performance. A product-stage figure covering only A1 to A3 is much lower than an upfront figure covering A1 to A5, which is lower again than a whole-life figure including replacement and end of life. Comparing across those boundaries tells you nothing about the buildings.
Multiply by the floor area on the same basis the intensity was calculated on — which is exactly where the area-definition question bites. Mixing a gross-internal intensity with a net-internal area produces a total that is wrong by whatever the difference between them happens to be.
Yes — the unit conversion is indifferent to what the carbon represents, so it applies equally to operational intensities in kg CO₂e per square metre per year. Just keep the time basis attached, since an annual operational figure and a one-off embodied figure are not comparable however they are expressed.