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Estimating and costing; principle of units

Short answer

Estimating calculates quantities from drawings and specifications; costing multiplies them by rates and adds overhead, profit, contingency and taxes. Units are chosen by geometry: m for linear work, m² for area work, m³ for volume work, numbers, weight, and lump sum. Measurement is net work in place.

What is estimating and costing? Explain the principle of units.

Estimating and costing

Estimating is calculating the quantities of the items of work and the materials required, from drawings and specifications. Costing is finding the cost of these quantities by multiplying them with the proper rates (rate analysis), and adding overhead, profit, contingency and taxes. Together they give the probable cost of a project before construction.

Principle of units

Each item of work is measured in the unit that suits its geometry, and that same unit is used for payment:

  • Length (m): cornice, skirting, railing, pipes, drains.
  • Area (m²): plastering, flooring, painting, formwork, roofing sheets.
  • Volume (m³): excavation, concrete, brick and stone masonry, filling.
  • Number (nos./set): doors, windows, W.C., lighting points.
  • Weight (kg/tonne): reinforcement, structural steel.
  • Lump sum: items that cannot be measured.

The measurement is of the net work in place; the description of the item covers materials, labour and tools included in the rate.

✓ Answer checked by Claude Opus 5.5 (high effort)

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