In the last 90 days, 4 listings have been listed, which means listings most likley are leasing quickly. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around sqft. Most properties in this area are around 21 floors. Most buildings in this region were built in 1927 and are Class A.
Not much of the real estate is used for commercial space, so it might be hard to find office space. Waste services is the dominant industry in this market. Most of the residents of Rittenhouse Square work from home. Commuting close to 15 minutes a day is the norm for those who opt to reside in this part of town.