When purchasing a tractor, how to determine engine horsepower based on the PTO power requirement of matched implements?

• PTO power is typically 85%-90% of engine hp; base selection on implement rated PTO demand.
• Rotary tiller needs about 12-15 PTO hp per meter width; back-calculate engine hp.
• Keep 15%-20% power reserve; avoid engine droop over 10% under heavy load.
• Verify PTO speed 540/1000 rpm matches implement spline specification.
• Request PTO shaft-end power test report, not just nominal horsepower.