Ahead of a refinement session, the Product Owner arrives with sizes already written against nine Product Backlog items, explaining that they sized them from last quarter's similar work to save the Developers an hour. Who is responsible for the sizing of Product Backlog items?

Professional Scrum Master I, objective 3. Managing products with agility easy

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The options

Not correct The Product Owner, since sizing feeds directly into ordering by value and cost

Wrong. Cost information genuinely does inform ordering, which is why this feels right, but the Product Owner consumes the size rather than producing it.

Not correct The Scrum Master, who facilitates estimation and keeps it consistent across Sprints

Wrong. A Scrum Master may help a team find a technique that works, but they hold no estimate of their own and do not standardise numbers on the team's behalf.

Not correct The Scrum Team as a whole, by consensus across all three accountabilities

Wrong. Several things in Scrum are the whole team's — the Sprint Planning result, the Definition of Done in the absence of organisational standards — but sizing is named more narrowly than that.

Correct The Developers who will be doing the work

Correct. The Guide assigns sizing to exactly the people who will carry it out, because only they can judge what the work costs them with their skills, their code and their Definition of Done.

Why

Sizing is a forecast about the effort of doing something, so it belongs to the people who will do it — a size produced by anyone else is a wish. That does not shut the Product Owner out: they may influence the Developers by helping them understand and select trade-offs, which is a conversation about scope and options, not a number handed over. Pre-filled sizes on the way into refinement are the classic wrong answer.

Where this comes from

Cited
Scrum Guide section Product Backlog
What it says
The Developers who will be doing the work are responsible for the sizing.

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