I used 1" for my sub panel roughly the same distance. I wished that I had used 1.5". Also while you have the trench open I always recommend laying a future pipe or two. You never know when you might need to run low voltage out there for alarm/cable/satellite, etc.
Future pipe is definitely a good idea. It's a common practice in commercial work for a reason. The extra cost of two spare 1.5" conduits is far less than the frustration of not being able to run whatever the heck you decide you need two years from now.
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