A break room without furniture doesn’t really serve its purpose of giving employees a place to relax and get away from their desks, so be sure to equip your break room with enough tables and chairs to accommodate a majority of your workers.
In the ideal world, every break room will be large enough so everybody in the company can be seated at the same time. Unfortunately, this is rarely the case, because most companies think of the break room as a luxury, not a necessity. Since it can help boost employee morale, a break room should be a requirement. If you cannot accommodate everybody at once, shoot for enough seats to hold half of the company comfortably. Since office workers usually take lunch at sporadic times, you should be able to fudge the numbers a little bit, but not by much.