Estimating and Costing: Methods, Formats, and Examples

Estimating and Costing Definitions

  • Estimating: It is the process of calculating the approximate quantity of materials, labor, and cost required for a project before starting the work.
  • Costing: It is the process of calculating the total expenditure of a project based on the estimated quantities, including material cost, labor cost, and other expenses.

Modes of Measurement in Construction

Item

Mode of Measurement

a) Brickwork

Measured in cubic meters (m³) for walls and structures.

b) Skirting

Measured in running meters (RM) or square meters (m²) based on height and length.

c) Earthwork

Measured in cubic meters (m³) for excavation and filling.

d) R.C.C (Reinforced Cement Concrete)

Measured in cubic meters (m³) for slabs, beams, and columns.

e) Formwork

Measured in square meters (m²) for shuttering and centering.

f) Dado

Measured in square meters (m²) based on surface area covered.

g) Woodwork for Door and Window Frame

Measured in cubic meters (m³) for solid woodwork.

Approvals and Provisions in Construction

  • Administrative Approval: It is the approval given by the concerned government authority for executing a project, ensuring its necessity and feasibility.
  • Technical Sanction: It is the approval given by an engineer or technical authority for the design, cost estimation, and specifications of a project.
  • Budget Provision: It is the financial allocation made by the government or organization for a project in the budget plan.

Key Considerations in Estimating

Rules for Deduction of Plastering Work (As per IS 1200)

  • Deductions are not made for openings (doors, windows, and ventilators) if the area is less than 0.5 m².
  • If the opening area is more than 0.5 m², the full opening area is deducted.
  • No deduction is made for ends of beams, small chases, and pipes up to 300 mm width.
  • For openings between 0.5 m² and 3 m², 50% of the opening area is deducted for one side plastering and 100% for both sides.
  • For openings more than 3 m², full deduction is made.

Standard Format of Different Sheets in Estimation

  • Abstract Sheet: Summarizes all quantities and costs.
  • Measurement Sheet: Details of item-wise measurements.
  • Rate Analysis Sheet: Cost calculation of materials and labor.
  • Material Requirement Sheet: List of required materials.
  • Lump Sum Sheet: Covers unexpected costs.

Checklist of Items of Work for Load Bearing and Framed Structure

  • For Load Bearing Structure:
    • Excavation and foundation
    • Brick masonry
    • Plastering and finishing
    • Flooring and roofing
    • Doors, windows, and painting
  • For Framed Structure:
    • Column footing and RCC columns
    • Beams and slabs
    • Masonry infill walls
    • Finishing and painting
    • Electrical and plumbing work

Role and Responsibilities of an Estimator

  • Preparing detailed estimates for projects.
  • Calculating material and labor costs accurately.
  • Ensuring cost control and reducing unnecessary expenses.
  • Following IS codes and specifications in estimation.
  • Checking measurement accuracy in BOQ (Bill of Quantities).

Approximate Estimate

Types of Approximate Estimate

  1. Plinth Area Estimate
  2. Cube Rate Estimate
  3. Unit Rate Estimate
  4. Approximate Quantity Method
  5. Bay Method
  6. Service Unit Method

Definition of Approximate Estimate

An approximate estimate is a rough calculation of the cost of a project based on previous similar works. It helps in deciding whether the project is financially feasible before preparing a detailed estimate.

Purpose of Approximate Estimate

  • To check feasibility of the project.
  • To get administrative approval from authorities.
  • To allocate budget for the project.
  • To compare costs of different projects.
  • To help in planning finance for government or private projects.

Approximate Estimate of Town Hall Building

Given:

  • Plinth Area = 1500 sq. m
  • Plinth Area Rate = ₹4000 per sq. m

Building Cost = 1500 × 4000 = ₹60,00,000

Now, additional costs:

Item

Percentage

Calculation

Cost (₹)

Water Supply & Sanitary

5% of ₹60,00,000

(5/100) × 60,00,000

3,00,000

Electrical Installation

10% of ₹60,00,000

(10/100) × 60,00,000

6,00,000

Other Services

5% of ₹60,00,000

(5/100) × 60,00,000

3,00,000

Contingencies

3% of Total Cost

(3/100) × (60,00,000 + 12,00,000)

2,16,000

Supervision Charges

8% of Total Cost

(8/100) × (60,00,000 + 12,00,000)

5,76,000

Total Estimated Cost = ₹74,92,000

Cube Rate Estimate for a Residential Building

Given:

  • Existing Building:
    • Plinth Area = 1200 sq. m
    • Height = 16.5 m
    • Cost = ₹6,00,00,000
  • New Building:
    • Plinth Area = 2900 sq. m
    • Height = 12 m

Cube Rate of Existing Building = Total Cost / (Plinth Area × Height)
= 6,00,00,000 / (1200 × 16.5) = ₹30,303 per m³

Estimated Cost of New Building = Cube Rate × New Plinth Area × New Height
= 30,303 × 2900 × 12
= ₹10,52,55,600₹10.53 Crore

Approximate Estimate for a Water Supply Project

Procedure:

  1. Determine Population Growth (using census data).
  2. Estimate Daily Water Demand (in liters per capita per day).
  3. Decide Source of Water (river, dam, well, etc.).
  4. Estimate Pipe Length and Size (for distribution network).
  5. Estimate Cost of Treatment Plant, Pumps, and Reservoirs.
  6. Consider Operation & Maintenance Costs.
  7. Apply Percentage Additions (contingencies, supervision, etc.).

Estimate for Two-Span Bridge

Given:

  • Existing Bridge Cost = ₹50,000 per meter
  • New Bridge Span = 40m × 2 = 80m

Total Cost = 80 × 50,000 = ₹40,00,000

Detailed Estimate

Data Required for a Detailed Estimate

  1. Drawings (plan, elevation, section).
  2. Specification of materials.
  3. Schedule of rates.
  4. Labour rates.
  5. Site conditions.

Definition and Purpose of Detailed Estimate

  • A detailed estimate is a complete calculation of all quantities and costs, including material, labor, transport, and other expenses, required for project execution.
  • Purpose:
    • To get technical approval.
    • To prepare tenders.
    • To control costs.

Types of Detailed Estimates

  1. Item Rate Estimate
  2. Revised Estimate
  3. Supplementary Estimate
  4. Annual Repair Estimate
  5. Special Repair Estimate

Contingencies and Work-Charged Establishment

  • Contingencies: Extra 3-5% amount added for unexpected expenses.
  • Work-Charged Establishment: Wages paid to workers directly engaged in the project (temporary staff).

Difference Between Revised Estimate and Supplementary Estimate

Feature

Revised Estimate

Supplementary Estimate

Purpose

Due to price increase or design changes

For additional works not included in original estimate

When Required?

If cost exceeds 5-10% of sanctioned estimate

If extra work is needed beyond the original plan

Example

Increase in material cost

Adding an extra room to a building

Long Wall and Short Wall Method for Quantity Calculation

Long Wall Method:

  • Outer dimensions of walls are considered.
  • Length = Centre-to-Centre distance + Half Breadth of Both Ends.

Short Wall Method:

  • Inner dimensions are considered.
  • Length = Centre-to-Centre distance – Half Breadth of Both Ends.

Example:
For a 4m × 3m room with 0.3m wall thickness:

  • Long Wall Length = 4 + (0.3/2) × 2 = 4.3m
  • Short Wall Length = 3 – (0.3/2) × 2 = 2.7m

Factors Considered During Detailed Estimate Preparation

  1. Site Conditions (soil, climate).
  2. Design and Specifications.
  3. Material Availability and Costs.
  4. Labour Charges.
  5. Machinery Requirements.
  6. Transportation and Taxes.
  7. Contingency and Overheads.

Provisional Sum, Prime Cost, and Day Work

  • Provisional Sum: Estimated cost for works where exact price is unknown.
  • Prime Cost: Cost of materials without including profit and overheads.
  • Day Work: Cost calculation based on actual labor and material used per day.