Relative estimation
Relative estimation sizes work items against each other (this story is twice as big as that one) rather than in absolute units (this story will take 6 hours). Story points, t-shirt sizes, and Fibonacci scales are all relative-estimation tools. The shared assumption is that humans are better at comparing magnitudes than producing absolute time predictions.
The cognitive evidence for relative estimation comes from the broader psychology of judgement: relative comparisons (which weight is heavier?) are systematically better-calibrated than absolute judgements (how many grams is this?). In software, relative estimation also sidesteps the trap of treating estimates as deadlines — points aren't hours, and a team's velocity (points completed per sprint) becomes the stable planning input regardless of how long individual stories take. Anti-patterns: comparing point scales across teams (a 5-point story means different things on different teams by design); converting points back to hours for capacity planning (defeats the entire purpose); treating velocity as a productivity KPI (incentivises point inflation).
Related terms
- Story points
A story-point estimate is a unit-less measure of relative effort assigned to a user story.
- T-shirt sizing
T-shirt sizing is a relative-estimation technique that assigns work items to size buckets — XS, S, M, L, XL — instead of point or hour estimates.
- Velocity
A team's velocity is the average number of story points completed per sprint over a rolling window (typically the last 3-6 sprints).