Estimation

Estimation in project management is the art and science of predicting how much effort, time, or resources a piece of work will require. In Agile, estimation is typically relative (comparing items to each other) rather than absolute (predicting exact hours).

Estimation approaches:

• Story points: Relative sizing using a numeric scale (often Fibonacci: 1, 2, 3, 5, 8, 13, 21)
• T-shirt sizes: Quick relative sizing (XS, S, M, L, XL)
• Planning poker: Team consensus estimation using cards
• Affinity estimation: Quickly grouping items by relative size
• Three-point estimation: Optimistic, most likely, and pessimistic estimates
• Analogous estimation: Comparing to similar past work
• Expert judgement: Based on experienced team members' knowledge

Story point considerations:

• Effort required (how much work?)
• Complexity (how hard is it?)
• Uncertainty (how much do we not know?)
• Risk (what could go wrong?)

Estimation best practices:

• Estimate as a team (collective wisdom is more accurate than individual guesses)
• Estimate relative to a reference story (calibrate against a known item)
• Do not convert story points to hours (they are not equivalent)
• Track accuracy over time and adjust
• Use estimation to drive conversations about scope and complexity
• Accept that estimates are approximations, not commitments
• Re-estimate when significant new information emerges

The #NoEstimates movement argues that estimation effort can be reduced by making all stories approximately the same size (small) and using throughput (stories completed per sprint) rather than story points. This approach works well for mature teams with consistent story sizing.