As Estimation is a core part of any industry growth so on what factors a estimator should consider for estimating project using thumb rules.?

In terms of Cost estimations - It all depends upon what are your direct and indirect costs for the project you are to be worked on

n estimator in the construction industry is responsible for compiling estimates of how much it will cost to provide a client or potential client with products or services. He or she will do this by working out how much a project is likely to cost and create budgets accordingly.

An estimator might work from a bill of quantities (the document outlining the basics of the work to be done) or just a set of drawings from the client. Estimators provide prices for everything from a one-off scheme to maintenance projects which will be completed over several years. 

An estimator is concerned with getting the best price that will win the contract in a competitive bidding situation, while ensuring that the contract can be carried out profitably. The best price isn’t always the lowest one, and clients now award contracts based on quality of the service offered, as well as cost. So, when bidding for new work, a quality submission is included along with an estimated price.

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estimation by rule of thumb is not totally accurate however, it is commonly used by estimators since it is the fastest way to produce an estimates and it is also derived from previous experience. Factors affecting this type of estimates are availability of resources, critical works, nature of works, planning ang etc.

-DRAWINGS

- B.O.Q.

SPECFICATIONS

-UP DATED MARKET PRICE

MATERIAL- MANPOWER

SUBCONTRACTORS PRICE

OVERHEAD

PROFET

RISK

i agree above answer mention the top answer

Thanks for invitation, and I am really sorry for my late, because I were  had a lot of work.

Estimations can be made between ratios of efficacy e.g. physical execution, financial execution. These can be plotted over time to determine their correlation, or establish a regression pattern to determine future tendencies.