You're better off guesstimating yourself than trusting contractors. The contractors are incentivized to severely oversize any AC units they install or else people leave bad reviews on their pages/listings when the installed unit can't keep up the one day every two years that the temperature gets abnormally hot.

I did this myself and insisted on a unit half the capacity that the contractors wanted. Several flat-out refused. But it works perfectly! Approximately one day ever two years it can't keep up. Which means that all the other time it doesn't short-cycle. Perfect.