Hobonichi’s size names are easy to remember and easy to misread. The important question is not which book is largest. It is how much space you need, where you will carry it, and whether your system is daily or weekly.
The four useful choices
Original or Planner: compact daily pages
The A6 family fits in the hand and works when you want one page per day without carrying a large book. It suits short journaling, a small daily log, and planning that stays close to the essentials.
Cousin: daily and weekly space
The A5 Cousin is the generous option. It gives you more room for writing, pasting, and a broader weekly overview. It is better for desk use than for a pocket or light commute.
Weeks: wallet-sized weekly planning
Weeks uses a horizontal weekly spread with a blank graph page beside it. Hobonichi describes it as a portable format for work and everyday planning. It is the choice for appointments and lists, not a full daily diary.
Weeks Mega: weekly planning plus a notebook
Weeks Mega keeps the portable weekly structure and adds nearly three times the memo pages of standard Weeks. That extra space helps if the planner also carries meeting notes, lists, or collections.
A simple decision test
Choose the smallest format that can hold your normal week. If you write a paragraph every day, start with a daily book. If you need appointments and a few notes, start with Weeks. If you regularly carry loose notes, consider Weeks Mega or Cousin.
The Jibun Techo vs. Hobonichi comparison covers a different decision: planning philosophy. Use this page for physical format and writing space.
The short answer
Original is compact daily planning, Cousin is spacious daily planning, Weeks is portable weekly planning, and Weeks Mega adds a large memo section. Choose the layout before the cover.