Assuming that you are asking about the average price per internal square foot, e.g. living area, for residential properties, many agents simply do not specify this on the multiple list service. When it is shown, it is sometimes under or overstated, and usually correlates directly with what is shown in the tax record, which is typically derived by measuring the exterior dimensions of the dwelling. If two stories, the assessor will multiply by 2. This doesn't truly reflect the actual living area, because that is derived by removing common areas from the total.
Having said that, I did look at the last 3 months of closed sales (4 of them for detached, fee simple homes) in zip code 21230. I did not include one of them, because the home was boarded-up. The three others appeared to be livable condition. Here are the stats:
Average Original List Price: $164,933
Last List Price Prior to Sale: $156,967
Average Closed Sales Price: $151,667
Next, I looked at each of the tax records and derived the average square footage of the three as 1487 sqft. Based upon the average of actual closed prices, the cost per sqft is approximately $102.
Please note that this price does not reflect any property which includes ground rent. In other words, the figure only reflects an average of the three most recently sold detached homes owned in fee-simple.