Project Sizing & Estimation


Project size and project estimate are numbers that decides a project’s life cycle. These numbers are the most important inputs for various activities like Project Planning, Resource Planning, Project Internal deadlines and Project Cost.

Difference between Project Size and Estimate

Quite often, these terminologies are confused as ‘Project Estimate’. Firstly, project size is represented in function points, use case points, source lines of code (SLOC) or components. Whereas Project Estimate is represented in man hours (mH) or man days (mD). Secondly, project size is a vital input for project estimation.

Sometimes a project is estimated from application scope statement without sizing which leads to problems like unknown estimation assumptions and inability to quantify change.

Project Sizing

Project sizing is primarily done for Project Estimation, Project Productivity Measurement and Project Progress Tracking. There are two ways to approach project sizing – counting the size of solution and/ or counting the size of requirements. New technologies are smarter and tend to have much less SLOC compared to their predecessor technologies and can be misleading. Lets look at project sizing for various types of projects:

1. Custom Development

Project sizing for a custom software development is achieved by considering:

  • Use case types (CRUD, Query, Transactional)
  • Complexity of use case
  • Number of alternate flows.
  • Number of screens and their complexities
  • Number of reports and their complexities
  • Number of significant business rules

2. Application Integration Development

Project sizing for an application integration development is achieved by considering:

  • End point systems/ applications
  • Services/ Adapters
  • Communication
  • Data Processing/ Transformation
  • Business Process Management

3. BI Projects

BI Projects are sized by considering schema and flow points (source, staging, ODS, DW, Data Mart and BI)

4. Data Migration Projects

For Data Migration Projects below elements are considered:

  • Source systems data migration points
  • Target systems data migration points
  • Number of source systems
  • Data Processing/ Transformation

5. Business Process Management

BPM Projects consider the below elements for project sizing

  • Use case points
  • Application Integrations

6. Configuration Package Projects

Configuration package projects like Oracle and Peoplesoft should consider the below elements:

  • Number of application suites
  • Number of module groups
  • Number of modules
  • Number of process points
  • Number of business units

Project Estimation

Project estimation is where we calculate the actual effort needed to complete the size. Following are the approaches:

1. Bottom Up Approach

The Bottom Up approach starts with detailed project activities keeping in mind the project components. Each of the project activities/ components are then summed up to calculate the phase or project estimates.

2. Top Down Approach

The Top Down approach uses the entire project size, project constraints, assumptions and risks to generate an effort estimate for the entire project. Phase estimates are then estimated using standard ratios.

3. Expert Judgement

An Expert creates the project estimation based on his past experiences with similar projects.

Ideally there is nothing called actual estimate. It is always advised to calculate various estimates for a project and validate them with one another.

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