Which measurement standard is right for your project and why does it matter?
Accurate floor area measurements aren’t just numbers — they affect property value, design, compliance, and investment decisions.
The notes in this article are based on the following two key guidance documents:
• RICS standards for NIA, GIA and GEA in their Code of Measuring Practice (CoMP). Full standard here: Code of Measuring Practice, 6th edition
• The IPMS Coalition IPMS standards for 1, 2, 3.1, 3.2, 4.1 and 4.2. Full standard here: IPMS All Buildings - final.pdf
NIA (Net Internal Area)
Measures the usable space within a building.
Ideal for: Valuation, letting and business rates for offices and retail space
✅ Includes: Office and retail space, kitchens, partition walls (where in sole occupancy), store areas.
❌ Excludes: Structural walls, communal corridors, toilets, stairwells, lifts
GIA (Gross Internal Area)
Measures total enclosed space within the building’s perimeter, not including the external wall thickness.
Ideal for: Industrial units and warehouse valuation and letting, business rates, service charge calculation.
✅ Includes: Internal walls, corridors, service areas and stairs.
❌ Excludes: Thickness of external walls, balconies, fire escapes, canopies
GEA (Gross External Area)
Measures the full footprint of the building including external wall thickness.
Ideal for: town planning, building cost estimation, council tax banding
✅ Includes: perimeter wall thickness, internal walls, columns, stairs
❌ Excludes: External balconies, fire escapes, canopies, open parking or terraces
IPMS (International Property Measurement Standards)
A global standard for consistent measurement across markets.
Published by the IPMS Coalition and approved by RICS.
Ideal for: International property portfolios, cross-border investments.
Key note: IPMS 2 and IPMS 3 include measurements to the Internal Dominant Face (IDF) which is ‘the inside surface area comprising more than 50 per cent of the lowest 2.75 m measured vertically from the structural floor surface, or to the ceiling if lower’.
This differs from the RICS internal wall measurement which is taken either to the inside face of the external wall if brick/block, or the glazing if it is full-height.
IPMS 1: Similar to RICS GEA but includes balconies.
IPMS 2: Similar to RICS GIA but measured to the IDF.
IPMS 3.1: Similar to RICS GEA but broken down by exclusive occupier with areas of exclusive occupation measured externally.
IPMS 3.2: The same exclusive occupations but measured to the internal dominant face.
While the measurements for a building to IPMS 1 or 2 will not change unless the building is structurally changed, the measurements for IPMS 3 and 4 will change dependent on the makeup of occupiers and the configuration of their demises.
IPMS 4 allows the user to define their own measurement extents to define the uses of different areas which may not be divided physically, for example front of house and back of house. It is worth noting that internal measurements for IPMS 4 are taken to the finished surface of perimeter walls rather than the IDF, which is more comparable with the RICS approach for NIA.
IPMS 4.1: Includes all internal walls and columns
IPMS 4.2: Excludes the internal walls and columns
Choosing the Right Standard
Different projects, different needs:
|
Standard |
Scope |
Common Use |
Includes |
Excludes |
|
NIA |
Usable inernal area |
Lettings/valuation (UK) |
Occupied Space |
Shared/common areas, walls |
|
GIA |
All internal space within walls |
Warehouse, industrial |
Corridors, toilets, internal walls |
External wall thickness |
|
GEA |
External footprint |
Planning, costing |
Everything to outer walls |
Open external features |
|
IPMS |
Varies by type (1, 2, 3.1, 3.2, 4.1, 4.2) |
Global standardisation |
Varies by type |
Varies by type |
Final Thoughts
The type of survey requested by a client can significantly affect the area of a property, so it is vitally important to carefully consider which standard is applied.
Our experienced team is here to help if you need precise, relevant and compliant floor area measurements. Just get in touch!
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