Fibonacci vs T-Shirt Sizing: Which Estimation Scale Should Your Team Use?

When your team sits down for sprint planning, one of the first decisions is what scale to use for estimation. The two most common are Fibonacci numbers (1, 2, 3, 5, 8, 13, 21) and T-shirt sizes (XS, S, M, L, XL). Each has a different sweet spot.

Fibonacci Numbers

The Fibonacci sequence is the default for most scrum teams because the increasing gaps reflect a real truth about software estimation: the bigger a task, the less precisely you can size it.

Pros:

• Fine-grained enough to distinguish a 3-point story from a 5-point one
• Directly feeds velocity tracking (add up points per sprint)
• Familiar to most developers who have used Jira or similar tools

Cons:

• Teams sometimes debate whether something is a 5 or an 8 for too long (here's how to resolve those stand-offs)
• Points accumulate meaning over time, making cross-team comparison misleading

T-Shirt Sizes

T-shirt sizing trades precision for speed. It works best for high-level roadmap planning when you need rough buckets, not sprint-level detail.

Pros:

• Faster to converge - fewer options means less debate
• Non-engineers find them more intuitive
• Forces teams to avoid false precision on uncertain work

Cons:

• Can't be summed for velocity tracking without a mapping (S=2, M=5, etc.)
• "Large" means different things to different people

How to Choose

If your team is new to estimation, start with t-shirt sizes to build the habit, then graduate to Fibonacci once everyone is comfortable with the process. For the rest of the technique family - affinity estimation, the bucket system, and where each one fits - see the agile estimation techniques guide. Whichever you pick, calibrate the scale against real stories so the values mean the same thing to everyone.

(Comparing poker against non-poker methods instead? See three-point estimation vs planning poker.)

One More Point supports both scales - pick the one that fits the meeting.