T-Shirt Sizing is a technique used for relative estimation and high-level sizing of items. You use this technique of relative estimation as opposed to absolute estimation when you just need a rough estimate or comparison of items. Speed is valued over accuracy which stops people from overthinking and overanalyzing, as you just want people to use their instincts and gut feeling. Information may not be available at this point anyway for detailed estimates. It is therefore used early on in agile projects or when there are a lot of items to estimate in a relatively short time.
** Note: If you need detailed estimating and sizing such as in Sprint Planning, it is better to use Planning Poker or other detailed estimation techniques.
You can have as many t-shirt sizes as you like, but best to keep it simple as it's only a rough estimate. The most common amount is 4 - Small, Medium, Large and Extra-Large.
How to Use:
Make up cards for each person using paper with a different t-shirt size on each card, S, M L, XL. This works just as well in-person and remotely if using videoconference. If remote, get each person to do this themselves.
As a team, work out what unit the t-shirt sizes represent, such as complexity, time taken to complete an item, cost, importance, or a mix of these.
Start with a small item so that everyone acknowledges how ‘Small’ is defined.
Repeat this next process until all items are estimated:
Select the next item to estimate. Compare that item with the last to determine the relative size.
Each person holds up a card to vote at the same time so as not to influence each other.
Take the average size that t-shirt size to that item.
If the item is too big, try to break it down into smaller user stories and estimate again.
When to Use:
During Ideation to measure value or importance.
During Product Backlog Refinement to prioritise items.
For other facilitation tools and techniques, refer back to the Facilitation Techniques Index.
To see how you can use these techniques in your Scrum Events, refer to our Scrum Events Facilitation Tools article.
ADDITIONAL READING Essential Scrum - Kenneth S. Rubin
This chapter describes the concept of estimation (and velocity) and its use in Scrum. A very short chapter and worth a read.
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