Quantity Surveying

Quantity surveying (taking off quantities) measures the amount of each item of work from the drawings so it can be priced. Accuracy and a systematic method are essential because errors here carry straight into the cost estimate.

Two standard methods measure building quantities: the centre-line method, quick for symmetrical buildings using the total centre-line length of walls, and the long-wall/short-wall method, which handles walls of different lengths and thicknesses. Both must correctly handle wall junctions.

Standard formulae speed the work — the steel bar weight D²/162 kg/m, brick counts per unit volume, and earthwork volumes by the trapezoidal or prismoidal rule. Deductions for door and window openings and other voids follow the measurement rules of IS 1200.

(prismoidal more accurate)

(D in mm, HYSD bar)

Relation 1 —

(prismoidal more accurate)

Write this relation with symbols exactly as in Estimating & Costing — BN Dutta before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 2 —

Write this relation with symbols exactly as in Estimating & Costing — BN Dutta before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 3 —

(D in mm, HYSD bar)

Write this relation with symbols exactly as in Estimating & Costing — BN Dutta before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

The centre-line method computes the total length of the centre line of all walls and multiplies by the cross-sectional area of the item (foundation, masonry); its advantage is speed, but at junctions the centre-line length must be adjusted (deducting half the wall thickness per junction) to avoid double counting.

The long-wall/short-wall method measures the longer walls out-to-out and the shorter walls in-to-in (or vice versa depending on the item), automatically handling the overlap at corners; it is more general when walls differ in length and thickness.

Standard weight and volume formulae come from geometry and material properties: the reinforcement weight formula D²/162 derives from the density of steel, and earthwork volumes use the trapezoidal rule (average of end areas) or the more accurate prismoidal formula for varying sections.

IS 1200 (method of measurement) standardises what is measured net and what deductions are made — for example small openings may be ignored while larger ones are deducted — ensuring consistency between the estimator and the contractor’s bill.

State assumptions explicitly before using any relation for quantity surveying — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.

Wrong assumptions invalidate the entire solution even when the formula is correct. In Estimation & Costing viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

1. Read the question and list given data with SI units (common in Estimation & Costing papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to quantity surveying.
4. Use equation 1: .
5. Use equation 2: .
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Quantity Surveying appears in tendering and project billing. In Indian civil curricula this topic is tested because it connects theory to quantity surveying and valuation.

GATE and semester exams often combine quantity surveying with earlier units — revise prerequisites before attempting mixed problems.

Industry interview panels sometimes ask: "Where did you use quantity surveying?" — answer with a lab, mini-project, or plant visit example if possible.

• Double counting or omitting wall junctions in the centre-line method.
• Mixing up which walls are measured out-to-out versus in-to-in.
• Forgetting deductions for openings as required by IS 1200.
• Misremembering the steel weight formula (D²/162, not D²/160).

Before attempting quantity surveying problems, confirm you can:

1. Centre-line method for symmetrical buildings
2. Long wall–short wall method for different wall lengths
3. Deductions for openings above certain size per IS 1200

Revise the solved examples in Estimating & Costing — BN Dutta and one previous-year GATE or university paper for this unit.