ESTIMATION

Built-up Area

Carpet area plus wall thickness + balconies (≈ plinth area of the unit)

Also calledbuilt up areaplinth areacovered area
Related on InfraLens
CODES
IS 3861
Definition

Built-up area is the total covered floor area of a unit including the carpet area plus the area occupied by the unit's own walls (internal and the unit's share of external/party walls) and its balconies and terraces. It is broadly equivalent to the plinth area attributable to the unit and is typically 10-15% larger than carpet area.

It sits between carpet area (net usable) and super built-up area (which loads in a proportionate share of common lobbies, staircases, lift wells, generator room, etc., often via a 'loading factor' of 1.25-1.45). IS 3861 'Method of measurement of plinth, carpet and rentable areas of buildings' is the Indian Standard governing how each is computed, important for billing, tax and tendering consistency.

Where used
  • Construction cost estimation (₹/sq ft of built-up)
  • Approval drawings + FSI/FAR computation
  • Property tax (many ULBs assess on built-up)
  • Contractor billing for civil works
  • Comparing developer quotes alongside carpet area
Acceptance / threshold
Computed per IS 3861. RERA still mandates that the legally binding sale figure is carpet area; built-up and super built-up may be shown for reference only.
Frequently asked
How much more is built-up area than carpet area?
Typically 10-15% more — built-up adds the unit's wall thickness and balcony areas to the net carpet area.
Is built-up area used for FSI calculation?
FSI/FAR is generally computed on the total covered (built-up) area of all floors divided by plot area, subject to the deductions each city's bye-laws allow (staircase, lift, services etc.).
Related terms
Carpet Area
Net usable floor area within walls; the RERA-mandated sale basis
Abstract Estimate
Cost estimate at concept stage based on plinth area or per-bed/per-room rates. ±20% accuracy.
Detailed Estimate
Quantity-based estimate from drawings. Each work item × unit rate × quantity = cost. ±5% accuracy.
Bill of Quantities (BOQ)
Itemised list of work activities with quantities and unit rates — forms the priced contract document.
Rate Analysis
Computation of unit rate from material + labour + plant + overhead + profit. Reference: DSR, state SOR, in-house DB.
Quantity Estimation
Estimate cement, steel, sand, aggregate for given area
U-Value (Thermal Transmittance)
Rate of heat transfer through a building element per unit area per °C, in W/m²·K. Lower U-value = better insulation.
Thermal Conductivity (k-value)
Heat conducted through a unit thickness of material per unit area per °C temperature difference, in W/m·K
Contingency
Provision for unforeseen costs. CPWD: 3%. Private: 5-10%. Higher for renovation than new build.
Strip Footing
Continuous footing under a load-bearing wall — width = wall thickness + 150 mm projection on each side.