Automation is quickly becoming the key to achieving the agility to truly embrace digital transformation, however working out the effort required for an automation project can be difficult. The individuals in each team may have different abilities and skillsets causing the estimates of tasks to differ. One way we can get around these added challenges is by using T-shirt sizes. By removing the focus on hours, days, weeks or any other numerical score, you don’t need to worry about the absolute time or effort – instead the estimates are based on past experiences and categorised – these categories are now our T-shirt sizes. This blog explores the use of T-shirt sizes and provides insight into how they can be used within an automation project.

Why a T-shirt?

The T-shirt size concept has been developed as way to estimate the effort required for automation projects. The primary advantage to T-shirt sizes is the speed and ease of getting started and being able to become familiar with relative estimating.

By expelling the focus on a numerical score, the development team has the ability and freedom to think more dynamically and abstractly about the effort associated with a request. By limiting the number of T-shirt sizes, you allow for faster estimates and less deliberation around placement. You can use T-shirts without a numerical value associated with them, but with values you can better identify the differences in size between the T-shirts and use those same values for pricing and velocity calculations.

What is a T-shirt?

A T-shirt is a defined amount of effort, measured in days, hours, points, or anything else you feel appropriate. These types of estimates become more efficient and effective when you have lots of ‘things’ to estimate at the same time, rather than just a single ‘thing.’

Behind a T-shirt size you often have a numerical value associated to it, this can be Fibonacci numbers or hours and days. So, for example, if you believe the new requirement will suit a medium T-shirt size, you now have an idea of the effort that will be required. The table below shows an example of T-shirt sizing using days of effort per T-shirt size.

T-shirt Sizing Table

SizeEffort (days)
Extra-LargeEstimated Per Requirement!


So how do we get started?

We’ve now worked out our T-shirt sizes and the numerical value associated to it, so where to from here?

  • We create a relative estimation. We do this by comparing the new requirement to a previous requirement
  • The old and new requirements are evaluated (at a high level) and a decision is made as to if they are equivalent in effort or not
  • If the old requirement had previously been gauged a ‘medium T-shirt’ and the new requirement doesn’t fit this size, well, you pick the right size T-shirt to fit the body!

Does it fit right?

During the development process you will get an idea if the estimate was accurate or not. If it’s way off adjust it accordingly. However, keep in mind that it’s also beneficial to keep with the initial estimate so that it can be reviewed afterwards against outcomes and enable you to understand what needs to be done to get better sizing next time.

When reviewing, the key questions to ask are:

  • Why was the initial estimate for the request sized as it was?
  • When the work was finished, what was the size more like?
  • Why was the request larger/smaller than expected?
  • What made this request the size it was? Was there just more work? Was this type of work new?
  • How can we avoid over or underestimating this type of request in the future?

Once you have reviewed your estimates against the reality (post-delivery) you can build out or adjust your baseline for each size. New requests from this point on will be based on this baseline.

How does Xtravirt use T-shirt sizes?

Often the information received during an automation project kick-off, is the name and a brief description of the Service Request (the thing that needs to be automated). The real detail is missing at this stage. Having such a small amount of information makes detailed planning difficult, you have questions that need to be answered, you don’t know the risks, full requirements or even the success criteria; yet you still need to provide two estimates to the customer – a cost estimate and an effort estimate.

This is where T-shirt sizes help us. We work with four sizes; small, medium, large and extra-large. Together as a team we go through the list of Service Requests, discuss what we believe may be required and provide our estimates. These estimates are based on previous experience and so afford us an educated idea on what size to allocate (relative estimation). When the team are agreed on the size of the Service Request we move on to the next until we have an estimate for all the required work. Once all the estimations are completed, we can provide an idea on the total effort, which then leads to an informed cost quote for the customer.

With our vast experience in delivering automation projects, we have gained a lot of historical information allowing us to analyse our decisions, see where we have over or under-estimated effort and identify why that happened. This provides us with the information required to ensure the original T-shirt still fits. If it doesn’t, we can change it for future estimates. Using this data, we can build out a baseline number of days associated to each T-shirt size.

Top tips

So, when looking at the effort for the automation project, my top tips are:

  • Create effort estimations before commencing any work
  • Record actual effort
  • Review actual vs estimated effort to better educate yourself for ‘next time’
  • Using terminology such as ‘T-shirt’ sizes help abstract away from hours, minutes, days of effort which is often hard to quantify
  • Continual refinement and education results in better estimation of effort and delivery cost as opposed to continually working with ‘Guesstimates’

Closing thoughts

Agility through automation is one of the most important components in a next generation IT strategy designed to meet current and future business needs. Without automation, IT will struggle to deliver value and keep up with the demands of the business. Successful automation is dependent on careful planning and scoping for level of effort and costs.

Xtravirt have a wealth of experience in scoping, planning, designing and deploying automation solutions and can help you find a solution that is right for your organisation and business needs. Contact us to find out more about how we can help.

Useful links

Case study: Automated processes speed up the delivery of IT infrastructure

Case study: Tailor made automation solution achieves efficiencies

Infographic: Why automate – key business benefits