Football fields actually make sense as a unit of measurement though. Unlike a lot of sports fields or arenas, American football fields have a very specific length and width: including end zones 360 feet long by 160 feet wide, approx 1.3 acres.

Furthermore, practically every American has hands-on experience with a football field. Almost every high school in America has one or has the use of a nearby one, some schools in inner cities might share. My high school had three, the stadium, the practice field, and the marching band practice grid painted on the student parking lot. Every student to attend the school spent at least some time on that field, for one that was the only venue on campus big enough to host the graduation ceremony. Several phys ed classes along with after school sports took place out there, as a band geek I spent entire weeks of my life on a football field.

So when you say to an American a field is 5 acres, unless they own significant parcels of land they can't really picture that, but tell them it's the size of 4 football fields they can pretty accurately picture that.