AGCO says 9 to 11 horsepower per foot width of implement.  To make the mental math easy, 10 hp/ft is a nice number to use.

https://www.masseyferguson.com/content/dam/public/masseyfergusonglobal/markets/en_us/assets/product-brochures/tillage/SF24BRC001AG_full%20product%20line%20up_brochure_11x8-5_LR.pdf

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