ESTIMATION

Quantity Estimation

Estimate cement, steel, sand, aggregate for given area

Also calledquantitymaterial quantityboqbill of quantities
Related on InfraLens
TOOLS
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READ
How Much Cement, Sand & Steel for a 1000 Sq Ft House?
TABLE
material quantitieswastage factors
Definition

Quantity estimation (also called quantity take-off, QTO) is the calculation of physical quantities of work for each BOQ item from drawings — concrete in m³, steel in kg, plastering in m², doors in numbers. The basis for project cost estimation, procurement, and contractor pricing. Per CPWD Manual + project specifications, quantity estimation requires careful drawing review and formula application.

Methods: (1) Long-hand calculation — formulas for each item (e.g., concrete volume = length × width × thickness). (2) Software-based — modern tools (Bluebeam, Vico, Tekla, CivilLane) automate. (3) BIM-based — quantities extracted from 3D models (Revit Quantification, Tekla, Vico). For a typical residential project, total person-hours for QTO: 200-500 hours depending on complexity. Typical accuracy: ±5% if drawings are detailed; ±10-15% if drawings are conceptual.

The most-overlooked aspect: completeness. Many BOQs miss items: secondary structural members, finishing details, MEP-related work, site preparation. Major Indian project cost overruns (10-30%) often trace to QTO incompleteness. Best practice: cross-checking by independent QS for major items; BIM-based extraction reducing manual errors.

Where used
  • BOQ preparation for tendering
  • Material requisition and procurement
  • Cost estimation and budget
  • Running bill quantity reconciliation
  • Variation order pricing
Acceptance / threshold
Per CPWD + project specification: every BOQ item with quantity from drawings; cross-check by independent QS for major items; reconciliation at running bill stage; final settlement variance analysis.
Frequently asked
What is quantity take-off?
Quantity take-off (QTO) is the calculation of physical quantities of work for each BOQ item from drawings — concrete in m³, steel in kg, plastering in m², doors in numbers. Used for project cost estimation, procurement, and contractor pricing. Modern software (Bluebeam, Vico, BIM-based tools) automates much of the process.
How are concrete quantities calculated?
Concrete volume = sum of (length × width × thickness) for each element from drawings. Add 5-10% wastage allowance. For complex shapes (curved walls, irregular slabs): break into rectangular pieces, sum up. Cross-check by computing volume by gross dimensions minus opening volumes (windows, doors, MEP penetrations).
What is the accuracy of quantity estimation?
Accuracy depends on drawing detail: with detailed shop drawings ±5%; with design drawings ±10%; with concept drawings ±15-25%. Best practice: BIM-based QTO reduces manual errors; cross-checking by independent QS catches transcription errors. Typical Indian residential project QTO takes 200-500 person-hours.
Related estimation terms
Construction Cost Estimation
Per sqft cost ₹1500-3500 in India
Material Wastage Factors
Cement 2-3%, steel 3-5%, tiles 5-10% typical
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.
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.
Contingency
Provision for unforeseen costs. CPWD: 3%. Private: 5-10%. Higher for renovation than new build.