Estimation and Sizing

Definition

Estimation and Sizing techniques approximate the effort, cost, time, or complexity required to deliver a piece of work. Approaches range from analogous estimation (comparing to similar past work) and parametric estimation (using historical data ratios), to relative sizing techniques common in Agile, such as story points or T-shirt sizing.

Inputs

• A defined work item, requirement, or backlog item needing an effort or size estimate
• Historical data, comparable past work, or team expertise to ground the estimate

Outputs

• An effort, cost, or relative size value assigned to the work item (e.g. story points, hours, T-shirt size)
• A basis for sprint planning, release forecasting, or budget approval

When to Use

• Planning capacity and sequencing for upcoming iterations or releases
• Comparing the relative cost of different requirements to support prioritization decisions
• Providing stakeholders with realistic delivery timeframes or budget expectations

When Not to Use

• Very early, undefined ideas where so little is known that any estimate would be misleadingly precise
• Single, one-off tasks where formal estimation ceremony exceeds the value of the estimate itself