Relation between T shirt sizing, story points, hours and when to use them #sizing #agile

The T-shirt sizing (XS, S, M, L, XL, XXL) is a popular estimation technique that often gets converted to story points. Here's how they typically relate:

Standard T-Shirt to Story Point Conversion

Common Mapping:

  • XS (Extra Small): 1 story point
  • S (Small): 2-3 story points
  • M (Medium): 5 story points
  • L (Large): 8 story points
  • XL (Extra Large): 13 story points
  • XXL (Extra Extra Large): 21+ story points

This often follows the Fibonacci sequence (1, 2, 3, 5, 8, 13, 21) which reflects increasing uncertainty in larger estimates.

[Each number is the addition of preceding 2 numbers]

T-Shirt Sizing to Hours (Rough Guidelines)

Typical Team Patterns:

XS Stories:

  • 1-4 hours
  • Simple bug fixes, minor text changes
  • "I can do this in half a day"

S Stories:

  • 4-8 hours
  • Small feature additions, straightforward tasks
  • "This will take me a day or less"

M Stories:

  • 1-3 days (8-24 hours)
  • Standard feature development
  • "This is a typical user story"

L Stories:

  • 3-5 days (24-40 hours)
  • Complex features, multiple components
  • "This will take most of a week"

XL Stories:

  • 1-2 weeks (40-80 hours)
  • Large features, significant complexity
  • "This might span multiple sprints"

XXL Stories:

  • 2+ weeks (80+ hours)
  • Epics that should be broken down
  • "This is too big to estimate accurately"

Practical Team Examples

Example 1: E-commerce Team

  • XS: Update product description (2 hours)
  • S: Add new filter option (6 hours)
  • M: Implement wishlist feature (16 hours)
  • L: Build recommendation engine (32 hours)
  • XL: Complete checkout redesign (60 hours)

Example 2: Mobile App Team

  • XS: Fix button alignment (1 hour)
  • S: Add new screen with basic layout (8 hours)
  • M: Implement push notifications (20 hours)
  • L: Build offline sync capability (40 hours)
  • XL: Integrate third-party payment system (70 hours)

Why T-Shirt Sizing is Popular

Advantages:

  • Intuitive - Everyone understands clothing sizes
  • Fast estimation - No complex point discussions
  • Less precision pressure - Harder to argue "Is it 5 or 8 points?"
  • Good for high-level planning - Perfect for roadmap discussions

When to Use Each Method

T-Shirt Sizing Best For:

  • Initial backlog grooming
  • Epic-level estimation
  • Stakeholder communication
  • Teams new to agile estimation

Story Points Best For:

  • Sprint planning
  • Velocity tracking
  • Detailed capacity planning
  • Mature agile teams

Hours Best For:

  • Task breakdown within stories
  • Individual work planning
  • Budget/resource planning
  • Client billing

Conversion Challenges

Team Variability: One team's "Medium" might be another's "Large" based on:

  • Team experience level
  • Technology stack complexity
  • Domain knowledge
  • Definition of "done" rigor

Story Type Differences:

  • Research spike M: 16 hours of investigation
  • Development M: 12 hours of coding
  • Integration M: 20 hours of testing/deployment

Best Practice Approach

Progressive Refinement:

  1. Epic level: Use T-shirt sizes for roadmap planning
  2. Release planning: Convert to story points for velocity planning
  3. Sprint planning: Break into tasks with hour estimates
  4. Daily work: Focus on task completion

Example Flow:

  • Epic: "User Authentication System" (XL = 13 points)
  • Stories: "Login UI" (M = 5 points), "Password Reset" (S = 3 points)
  • Tasks: "Create login form" (4 hours), "Add validation" (3 hours)

The key is using the right granularity for the right purpose - T-shirt sizes for big picture planning, story points for sprint commitment, and hours for daily task management.

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