If your team has ever debated whether to use story points or T-shirt sizes, you are not alone. Both methods are widely used, both work — and both fail in predictable ways when applied in the wrong context. Here is a direct comparison.
What is T-shirt sizing?
T-shirt sizing uses clothing labels — XS, S, M, L, XL, sometimes XXL — to bucket work into rough size categories. It is fast, intuitive, and requires almost no calibration. Anyone who has bought a shirt understands the scale immediately.
Teams use T-shirt sizing most often during roadmap planning, when stories are still vague and a precise estimate would be meaningless anyway. It answers the question: "Is this a small thing or a big thing?" without pretending to know more than that.
What is planning poker?
Planning poker uses a numerical scale — typically Fibonacci: 1, 2, 3, 5, 8, 13, 21 — where each number represents relative effort compared to a reference story. The key mechanic is simultaneous reveal: everyone votes at the same time, preventing anchoring bias.
Planning poker is designed for sprint-level estimation. It generates discussion, surfaces hidden complexity, and produces numbers that feed directly into velocity tracking.
Key differences
When to use T-shirt sizing
Use T-shirt sizing when you are working with epics or features that are too large or too undefined to estimate precisely. Quarterly planning sessions, product roadmaps, and early discovery conversations are all good candidates.
T-shirt sizing is also useful when you need to estimate a large backlog quickly — 50 items in 90 minutes, for example. You would never do that with planning poker.
When to use planning poker
Use planning poker when stories are well-defined enough to estimate and you need numbers that will feed your sprint capacity planning. The discussion it generates is a feature, not a bug — teams that use planning poker consistently report better shared understanding of what they are building.
The best teams use both. T-shirt sizing to groom and prioritize the backlog at scale, planning poker to estimate stories just before they enter a sprint.
Can you convert T-shirt sizes to story points?
Yes, and many teams do. A common mapping: XS = 1, S = 2, M = 3, L = 5, XL = 8. The problem is that this conversion loses the nuance planning poker creates. An item estimated at L in a 10-second T-shirt vote might be a 5 or an 8 in planning poker, depending on what the discussion reveals.
Use the conversion as a starting point, not a substitute for the estimation conversation.
Which one should your team use?
If you are running sprint planning and need numbers your team will stand behind, use planning poker. If you are doing quarterly planning with 40 items and two hours, use T-shirt sizing. Most mature agile teams end up using both — at different levels of their planning hierarchy.