City lots in historic neighborhoods often have standard sizes. It can be broken down from a square mile that stands at 640 acres. A standard lot usually measures 66 feet wide by 132 feet deep. That equals .2 acres or 8712 square feet. Sometimes two houses are put into this lot, so it would be .1 acres with just 33 feet wide by 132 feet deep. Other times, especially in corner lots, a lot might measure just 33 feet by 66, which is .05 acres.
While these lot sizes are standard in many older cities, it is not always the case. Sometimes lot sizes are random, with some extra large lots or extremely small lots that once housed a carriage home. The image shows lot lines in a historic neighborhood taken from Zillow. Note how most lots are 66 feet wide by 132 deep, but with some variation.