Your question isn't quite clear on what you're trying to accomplish. Can you further describe your dilemma? Do you already know the total amount of rent that you wnat to charge? If that's all you're looking for, divide the total desired rent by the total square footage of the rented space. That is your per-foot rate, which could reasonably be applied to any other space of any other size, assuming that you are not discounting or charging a premium for smaller or larger spaces. Example: Unit 1 = 1,000 Square Feet and we charge $850.00 per month Unit 2 = 1,875 Square feet - we've not establishe the monthly rent for this unit, but we want it to be comparable to the basis of Unit 1. Here's your formula: GROSS RENT divided by GROSS SQUARE FOOTAGE equals PER FOOT RATE. Here's your formula in application: $850.00 divided by 1,000 sq. Ft = $0.85 per foot per month (your prescribed square footage rate). Since you've established your monthly per foot rate and you (presumable) are not discounting up upcharging unit 2 due to size, usability, curb appeal, etc., Unit 2's gross rent will likely be $1,600 per month (rounded up from $1593.75, which was we achieved by multiplying Unit 2's area, 1875 sq.ft. By $0.85 per foot) That is somewhat common math, so I'm guessing that this didn't address your question but since you asked for the "formula" specifically, I'm not exactly sure what else you might be looking for. If what you're looking for actually isn't the formula but mediane per-foot rental rate that would be deemed acceptable as well as salable in your local marke, there are some sources on the net (i.e. Realtor.com). You might run a search for rental properties currently seeking tenants- making sure that you are seaching for properties that have the same basic specs (footage, bedrooms, bathrooms, garage, yard, pool, etc.) You also have to consider neighborhood. In many cases you can have a house that demands a much higher rents that a virtually identical home in a neightborhood only a couple of blocks away. Get a general sampling of your specific area with your property type, and you'll come up with what the market is currently delivering. I hope one of these responses helps. I'd be happy to readdress the question if I've missed your intended question.
