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IS 3861:2002 is the Indian Standard (BIS) for method of measurement of plinth, carpet and rentable area of buildings. This standard provides a uniform method for measuring the plinth area, carpet area, and rentable area of buildings. It establishes clear inclusion and exclusion criteria for spaces such as balconies, staircases, lifts, and ducts to ensure standard calculation practices in architecture, real estate, and valuation.
Method of Measurement of Plinth, Carpet and Rentable Area of Buildings
Overview
Status
Current
Usage level
Frequently Used
Domain
Architectural — Methods of Measurement of Works of Civil Engg.
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! Engineers and architects must distinguish between IS 3861 Carpet Area (which excludes internal partition walls) and the RERA Carpet Area (which includes internal partition walls).
! Plinth area must include the external wall thickness and is measured at the floor level of any given storey.
! Open-to-sky courtyards, cantilevers, and un-enclosed porches are generally excluded from plinth area measurements.
Defines methods for measuring usable, rentable, and gross areas, primarily for commercial office leasing.
IPMS: Office Buildings 2023IPMS Coalition, International
HighCurrent
International Property Measurement Standards: Office Buildings
Provides a global framework for measuring office buildings, defining IPMS 1, 2, and 3 for gross, internal, and usable areas.
ISO 9836:2022ISO (International Organization for Standardization), International
MediumCurrent
Performance standards in building — Definition, calculation and expression of area and space indicators
Provides a framework and definitions for calculating various area indicators like Gross, Net, and Usable Floor Area.
PCA Method of Measurement 2020Property Council of Australia (PCA), Australia
HighCurrent
Method of Measurement for Lettable Area
Specifies methods for measuring lettable areas in commercial, retail, and industrial properties for leasing.
Key Differences
≠IS 3861's 'Carpet Area' explicitly excludes areas for kitchens and sanitary accommodations (toilets), whereas international standards like BOMA and IPMS include private kitchens and toilets within a tenant's 'Usable Area'.
≠The Indian concept of 'Plinth Area' (built-up area including all walls at floor level) does not have a direct one-to-one equivalent. It is similar to but distinct from BOMA's 'Construction Gross Area' or RICS's 'Gross External Area' due to different measurement points (e.g., at plinth level vs. external wall face).
≠BOMA standards provide highly detailed, prescriptive methods (Method A and Method B) for allocating common areas (applying a 'Load Factor' or 'R/U Ratio') to calculate 'Rentable Area'. IS 3861's definition for 'Rentable Area' is less prescriptive about the allocation methodology.
≠For 'Carpet Area', IS 3861 measures the area within the finished internal faces of the walls, completely excluding the walls themselves. In contrast, BOMA 'Usable Area' includes the area to the centerline of inter-tenant walls and to the inside face of the exterior glass.
Key Similarities
≈All standards aim to provide a consistent, repeatable methodology for measuring floor areas to facilitate property valuation, leasing, and management, thereby reducing ambiguity and disputes.
≈They all employ a hierarchical system of area measurement, typically starting from a gross overall area and progressively refining it to a net usable or rentable area (e.g., Plinth > Carpet vs. IPMS 1 > IPMS 2 > IPMS 3).
≈Vertical penetrations such as lift shafts and main stairwells are consistently excluded from the net usable/carpet area calculation across all standards.
≈Open-to-sky areas, unenclosed balconies, and open verandas are universally excluded from primary internal area measurements like Carpet Area, Usable Area, or Net Lettable Area.
Parameter Comparison
Parameter
IS Value
International
Source
Private Kitchens/Pantries
Excluded from Carpet Area.
Included in Usable Area.
IPMS: Office Buildings
Private Toilets
Excluded from Carpet Area (listed under 'sanitary accommodation').
Included in Usable Area.
ANSI/BOMA Z65.1-2017
Internal Partition Walls (within tenant space)
Area of walls is excluded from Carpet Area.
Included within Usable Area.
ANSI/BOMA Z65.1-2017
Columns / Structural Elements
Included in Carpet Area if freestanding within a room; area of columns forming part of a wall is excluded.
Included in Usable Area.
ANSI/BOMA Z65.1-2017
Common Area Corridors
Excluded from Carpet Area; a proportionate share is added for Rentable Area.
Excluded from Usable Area; a proportionate share is added to calculate Rentable Area.
ANSI/BOMA Z65.1-2017
Measurement of Rentable Area
Carpet Area + Wall Areas + Proportionate share of common areas.
Usable Area multiplied by a load factor/ratio (R/U Ratio) that represents the tenant's share of common areas.
ANSI/BOMA Z65.1-2017
Unenclosed Balconies
Excluded from both Plinth Area and Carpet Area.
Excluded from primary Rentable/Usable Area calculations; often measured and reported separately.
ANSI/BOMA Z65.1-2017
⚠ Verify details from original standards before use