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
- Plinth Area Estimate
- Cube Rate Estimate
- Unit Rate Estimate
- Approximate Quantity Method
- Bay Method
- 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:
- Determine Population Growth (using census data).
- Estimate Daily Water Demand (in liters per capita per day).
- Decide Source of Water (river, dam, well, etc.).
- Estimate Pipe Length and Size (for distribution network).
- Estimate Cost of Treatment Plant, Pumps, and Reservoirs.
- Consider Operation & Maintenance Costs.
- 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
- Drawings (plan, elevation, section).
- Specification of materials.
- Schedule of rates.
- Labour rates.
- 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
- Item Rate Estimate
- Revised Estimate
- Supplementary Estimate
- Annual Repair Estimate
- 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
- Site Conditions (soil, climate).
- Design and Specifications.
- Material Availability and Costs.
- Labour Charges.
- Machinery Requirements.
- Transportation and Taxes.
- 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.