I included a Product Backlog Estimation model to calculate a total price using my Definition Of Agile Planning. And on top of User Stories and Story Points the Sizing of User Stories is to be considered:
The right size of a User Story is 0,5-5 ideal days (di) (ideal time = Story Points). For development. To be invEST. To comfortably fit a Sprint.
- Epic Stories can be 5-15 di. A size not suited for development but acceptable for estimating. To be split into User Stories.
- Cosmic Stories are >15 di. They can serve only as a beginning to understand a Product, not for estimation or development.
- Tiny Stories are < 0,5 di. To be combined into User Stories.
Note: ‘Minimal Marketable Features’ (MMF) from Kanban can be a set of User Stories. Possibly an Epic Story.
The best base to estimate is experience. When experience is limited, use relative estimates (complexity scaling). I use a 1-2-5 scale:
- Size is set upon complexity to 1-2-5-10-20-50-100-… Always use the higher value if you end up in between two points.
- Find some reference points in your experience to compare.
- Refine until you end up with real estimates (Story Points).
note: Ideal time is development time without breaks, questions, problems or any interrupts. It is multiplied with Velocity to get Planning days.