What are different ways to size stories? Why do we do story points, not hours?

MIke Cohn talks a  lot about this in his book Agile Estimation and Planning. You can use any measure to size stories.

Teams use different sizing techniques:

T-Shirt Sizing

X Small, Small, Medium, Large , Xtra Large

or

Coffee Sizing

Small, Tall, Grande

You can pick any sizing technique. Make up one if needed.

This is mainly done as we as humans and as managers are better at abstract terms. If we use hours as a way to size stories,then the managers in the room have questions, teams dont immediately feel comfortable with hours.

Sizing keeps the planning meeting at a fast pace.

A general measure you can use  for T-Shirt sizing is how many days it take to complete a story

Small story –  1-3 days

Medium – 3- 5 days

Large – 5 – 7 days

X Large > 10 days

In order to convert a story size to a number, you can use either factorial, Fibonacci, or Squares.

If in a sprint your team does two small stories and two mediums then your velocity is 9 * 2 + 4 * 2 = 26 ( if you are following the squares technique). Square is simple and works quite well.