Quick decision table
Half-obi, pouch, doll, small tapestry → 2m. Nine-inch obi, haori, full tapestry, large tote → 3m.
2m projects
Most beginner and intermediate handmade projects fit comfortably in 2m × 110cm.
3m projects
A nine-inch nagoya obi finished face is around 3.6m × 31cm. Cutting from a 3m panel is feasible with careful layout.
Common pitfalls
Don't buy 2m if your project mentions "obi" — most obi shapes won't fit. Don't buy 3m if all you need is collars and pouches.