Estimate or Guesstimate?

  • Introductions
  • Why estimate?
  • How to estimate
  • Alternatives

Hands up …

  • If you have an appreciation of Agile?
  • Who follows the practices of Scrum?
  • Who has to provide estimates?
  • Who knows quantum mechanics theory?
  • Richard Herbert MSc CSM - [email protected]
  • Originally started in architecture and engineering
  • Got into computing via structural analysis
  • Moved into IT management
  • Been a freelance web developer since 2001
  • MSc Internet Systems Development
  • Certified Scrum Master since 2014
  • Available for weddings, christenings, Bar Mitzvahs and other Agile opportunities
  • I need all these features but…
  • How long will it take?
  • How many developers do I need?
  • How much will it cost?
  • Can I change my mind?
  • It's easy to estimate something that's well known, constrained and predictable
  • Increases in variability, interpretation and understanding causes doubt
  • Where there is doubt, there is delay
  • Where there is delay, there is cost
  • Naming things (49%)
  • Explaining what I do (16%)
  • Estimating time to complete tasks (10%)
  • The challenge:
    • guessing how long something, that you possibly haven’t done before, will take
    • making estimates based on vague requirements
    • trying to allot time for dealing with unforeseen problems

“In preparing for battle I have always found that plans are useless, but planning is indispensable”


“Plans are worthless, but planning is everything”

  • Goals or Epics
  • Features or Activities of each Goal
  • Tasks or outline Stories that form each Feature
  • Group Tasks into Releases
  • Short and to the point
  • Limited to an index card
  • Promise of a further conversation
  • Includes acceptance criteria
  • Estimated with Story Points

A promise of a further conversation

I Independent The user story should be self-contained, in a way that there is no inherent dependency on another user story
N Negotiable User stories, up until they are part of an iteration, can always be changed and rewritten
V Valuable A user story must deliver value to the end user
E Estimable You must always be able to estimate the size of a user story
S Small User stories should not be so big as to become impossible to plan/task/prioritise with a level of certainty
T Testable The user story or its related description must provide the necessary information to make test development possible
  • Can do
  • Give technical insight
  • Write technical stories
  • Define the test criteria
  • Definitely
  • Owns the Stories
  • Provides the detail
  • Defines the Acceptance Criteria
  • Justifies business value
  • Rarely
  • Advises
  • Guides
  • Facilitates
  • A polite word for a guess
  • Improves with experience
  • Cone of uncertainty

"The exact number of candies in this jar can not be determined by looking at it, because most of the candies are not visible. The amount can be estimated by presuming that the portion of the jar that cannot be seen contains an amount equivalent to the amount contained in the same volume for the portion that can be seen"

Linguist Geoffrey Pullum stated the quotation was "completely straightforward" and "impeccable, syntactically, semantically, logically, and rhetorically. There is nothing baffling about its language at all."

  • Not time but effort based sizing
  • Tee-shirt sizing (small, medium, large, x-large)
  • Trouser sizing (short, regular, long, x-long)
  • Dogs (Chihuahua, Greyhound, St Bernard, Great Dane)
  • Story Points
    • Relative sizing (1, 2, 3, 5, 8, 13, 21, 34)
  • Planning Poker
  • All show their hand at the same time
  • Discuss and justify variations
  • Agree the effort – if not, break the Story
  • Team Velocity
  • Initially a guess
  • Indication of capacity
  • Indication of completion
  • Burndown Chart

Story Points:
The separation of the estimation of effort from the estimation of duration

"Every year there is a new estimation technique. The real Agile approach would be to throw estimates out"
Ron Jeffries - Agile Manifesto co-author

  • A popular movement in the Agile world
  • Considers estimating a waste of time
  • "At the one point in the project when I know the least about it you want me to commit to a timescale and cost!"
  • A ship's Captain can only see as far as the horizon
  • Yesterday's weather
  • Look back over past work
  • Keep metrics on similar stories
  • Forecast based on experience
  • Track stories through the stages
  • Estimating is hard
  • It's often wrong
  • Practice can help
  • Don't commit too far into the future
  • Consider other approaches
  • The value needs to be proven




  • Richard Herbert
  • [email protected]
  • @agilemix
  • +44 (0)7717 846090