Label the number before comparing it
A horsepower figure needs a label to be useful. Engine horsepower and PTO horsepower describe output at different places on a machine. As a concrete example, John Deere lists the 5075EN with 75 engine horsepower and 58 PTO horsepower; those numbers describe the same tractor, not competing estimates.
Create separate comparison columns for engine power and PTO power. If a listing gives only a single horsepower figure, ask which rating it represents.
Compare like with like
When researching several tractors, preserve the rating description alongside each value. A published claim, a particular test result, and a different model-year specification should not silently become one interchangeable number.
Check the implement documentation for the power rating it actually specifies. Horsepower alone does not establish compatibility: connection type, operating speed, hitch requirements, weight, and the tractor configuration still matter.
Record what still needs confirmation
Use the model page as a starting point for questions. If the required PTO rating is missing, put it on your dealer or seller checklist rather than substituting engine horsepower. Keep a copy of the applicable tractor and implement manuals with your research so the final decision is based on a matched combination.