Cost and effort estimates are a central component of project plan development. For each listed task in your project activity definition, use resource planning data to develop effort estimates, in units combining staffing and time, such as person-days or engineer-hours. Useful sources to assist with estimating include:
History (lessons learned, databases of project diagnostic metrics, information from earned value management)
Activity owner analysis and personal experience
Analogs (previous work of a similar type)
Experts (consultants, peers, managers, vendor proposals)
Published data (WWW, papers, articles, professional magazines)
Parametric, or size-based formulas (“rules of thumb,” complexity analysis, component or module counts, ...