For many retail or commercial properties, parking ratios are frequently expressed as number of spaces ore thousand square feet of building..... i.e. - 4:1 would mean there are 4 parking spaces for each thousand square feet of building on a property. Using your example of 28 spaces, if the building was 7,000 sf, then the property has a 4:1 parking ratio. If instead, it was a 4,000 sf building with the same 28 spaces, the property would be parked at a 7:1 ratio. Although it's not my primary domain (I work mostly in retail restaurant), I would imagine there are similar nomenclatures for apartment properties and hotels where the ratio might be expressed as spaces per rental unit or lodging "key"' rather than against 1,000 sf. Hope this is what you were looking for.
May 4, 2011