Real Estate Forecasting: Measuring Real Estate. When forecasting properties, size is also relevant in addition to property type. While most spaces can be customized, sub-divided, and combined into larger spaces, smaller properties are easier to predict in terms of occupancy and cash flows. With larger properties the formula is more complicated, particularly in multi-floor buildings. In these properties, the floors can be subdivided or customized per tenant, and there are often many floors and many tenants. Floor plates keep track of the square footage per floor and stacking plans show the details of the leases themselves. Regardless of purpose, all leaseable real estate is driven by space, often measured by being squared. In the US this is in square feet, and outside of the US this is in square meters. Either way, the calculation is length times width. The gross area is the total interior floor area. Not all of this space will be usable as some of the space is shared and some of the space is used for utilities. Of course, the tenant or lessee will be concerned with the actual usable space, which is the net leaseable area. The difference is often the common areas such as elevators, passageways, restrooms, lobbies, and parking. Rental income is calculated by the market price per square foot or meter times the size of the space. Certain sub-sectors, such as residential and hotels have slightly different formulas, but in general, the larger the room or space, the higher the rent or rate. With multiple tenants in one property, pro rata calculations determine the way expenses or responsibilities are shared. A tenant's percentage of their NLA is their pro rata percentage. The common area is not included in this calculation, but the pro rata percentage will determine each tenant's share of the expenses, both of the building and in maintaining the common area.