In the meantime, the acre is the standard unit of area for farms, fields, residential property, other property, parks, and certain other uses of land. A house on a quarter-acre lot generally has a backyard, and would fit in most suburbs. A house on a half-acre lot has a big backyard with plenty of room for your kids to run around. A full acre is getting pretty decently big — it's more like the size of a small field that you'd use for growing crops (which is the origin of the measure: 1 farmer-pair-of-oxen-plow-day.)
Rain is measured in inches and feet.
Just multiply two values people use in practice and get another that they can use in practice: acre-feet. Are you forecast for three inches (0.25 feet) of rain, on your forty-acre property? That's 10 acre-feet of water you can get from the sky instead of the irrigation authority. Like most things customary, it's easier to use in some ways, harder in others.