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Definition, Purpose and Data Required for Estimation

Estimating
Estimating is the process of calculating the quantities of various items of work of any projects and finding the probable cost of the project by multiplying the quantities of various items of work with their respective rates.

Estimated Cost
It is the theoretical cost of the work or approximate/ probable cost of work. Quantities of various items of work are calculated from the detailed dimensioned drawings and the estimated cost is obtained by multiplying the quantities by their respective rates.

Actual Cost
It is the cost obtained after the completion of the work. Actual cost gives the actual expenditure of the work. It is generally obtained from accounts records.

Purpose of Estimating

  • To ascertain the reasonable accurate idea of the cost of work.
  • To determine the various types and quantities of the materials required during execution of the work.
  • To estimate the number of different categories of labors required to complete the work.
  • To access the requirements of the various types and quantities of the tools , equipment’s and plants required to complete the work.
  • To draw up the schedule of projects and ascertain the time of completion of the work or overall projects.
  • To justify the investment on any project from benefit cost ratio. (Benefit cost ratio should be greater than one for ideal investment)
  • For valuation of the existing property, an estimate is required.
  • To control the expenditure during the execution of the work.
  • To invites tenders and quotations and to arrange the contract.

Principle of Units of Measurements

  • For mass and voluminous work: cubical unit eg: Earthwork,Brickwork, Stone masonry, wood work etc.
  • For surface and thin work: square unit eg: Plastering, Flooring, Painting etc
  • For small but long item: linear unit eg: Skirting, Eaveboard etc
  • For piece work,job work : number eg: W/C pan, Basin, Tubelight, Socket etc.
  • For liquid: volume,liter eg: Paint, water etc.
  • For weighty items:- weight eg: Rod, Cement, Nail work etc.

Rules for Measurement

  • Measurement shall be made for the finished item of work and description of each item shall include materials, transport, labour, fabrication tools and plant and all types of overheads for finishing the work in required shape, size and specification.
  • In booking, the order shall be in the sequence of length, breadth and height or thickness.
  • All works shall be measured subject to the following tolerances.
    • Linear measurement shall be measured to the nearest 0.01 m.
    • Areas shall be measured to the nearest 0.01 sq.m
    • Cubic contents shall be worked-out to the nearest 0.01 cum
  • The Same type of work under different conditions and nature shall be measured separately under separate items.
  • The bill of quantities shall fully describe the materials, proportions, workmanship and accurately represent the work to be executed.
  • In case of masonry (stone or brick) or structural concrete, the categories shall be measured separately and the heights shall be described
    • from foundation to plinth level
    • from plinth level to First-floor level
    • from First floor to Second-floor level and so on.

Units of Measurement and Payment for Various Items of Works and Materials

Item no. Description of work Unit of measurement Unit of Payment
1. Earthwork    
a. Earthwork in excavation m3 Per 100 m3
b. Earthwork in filling in floor m3 Per 100 m3
c. Earthwork in filling/banking work m3 per m3
d. Earthwork in cutting in rod work m3 per m3
e. Surface dressing m2 Per m2
2. Brickwork    
a. Brickwork in flat soling m2 per m2
b. Brickwork in foundation m3 per m3
c. Brickwork in superstructure m3 per m3
d. Brickwork in cornice m3 per m3
e. Half- brick thick wall m2 per m2
3. Concrete work    
a. PCC in foundation m3 per m3
b. 75mm thick PCC m2 per m2
c. 50mm thick PCC m2 per m2
d. Lime concrete PCC m3 per m3
e. PCC for RCC works m3 per m3
4. Plaster works    
a. Cement plaster m2 per m2
b. Pointing works m2 per m2
5. Wood work    
a. Wood work for doors and windows m3 per m3
b. Wood work for doors and windows m2 per m2
c. Wood work for truss m3 per m2
d. Wooden partition m2 per m2
e. Wooden false ceilings m2 per m2
f. Wooden form work m2 per m2
g. Woodwork for rafter, joist,purlins, wall plates etc. m3 per m3
6. Metal works    
a. Mild steel grill kg per kg
b. Steel reinforcement for RCC works kg per kg
c. Tubular trusses and purlins kg per kg
7. Painting works(distemper,cement,plastic emulsion,enamel paint etc.) m2 per m2
8. Marble flooring m2 per m2
9. Cement skirting m per m

Data Required for Estimating

  • Drawings
    The basic thing needed for estimating is well-dimensioned drawings showing plans, different sections , and other relevant details for the work.From the drawings , quantities of various items of work are calculated.
  • Schedules of Rates
    Quantities of various items of work calculated from drawings are multiplied by rates to obtained the estimated cost. Therefore, rates are the vital factors in estimation. The rate of an item of work is variable according to time, situation , and other various factors.
  • Specifications
    1. General Specifications
      In order to know the general idea of the project we should describe the following:
      • Nature of work
      • Class of work
      • Names of materials
    2. Detailed Specifications
      Every item of work in the estimate is described in the detailed specification. Detailed specifications include specification of quantities, qualities and proportion of materials, type of machinery,equipment’s,tools and plants and their method of operation and so on. Specification for different items of work is maintained by engineering departments.
  • Updated Method of Measurements
    In order to determine the correct quantities of various items of work we should follow the updated method of measurement.

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