There is no official limit to the number of seat reservations you can make with a JAPAN RAIL PASS. You are entitled to unlimited seat reservations on eligible JR trains for the entire duration of your pass validity.

Fair Usage Guidelines:

While there is no numerical cap, JR encourages "fair usage" to ensure all passengers have access to seats:

• Avoid Double Booking: Please do not reserve multiple trains for the same time slot (e.g., reserving two different Shinkansen departures for the same morning).
• Return Unused Tickets: If your plans change and you cannot make it to your reserved train, please return the seat ticket to a JR ticket office or use the ticket machine to cancel. This allows the seat to be re-opened for other passengers.

Important Distinction:

Please note that for the Nozomi and Mizuho trains, you must purchase a separate supplement ticket for each ride. These specific trains are not covered by the "unlimited free reservation" rule of the standard pass.