Americans will do anything but use the metric system, they say. Americans also love football 🏈. Naturally, Americans often use football fields as a unit of length.

But usually, only large distances are described in terms of football fields. Americans don’t often say their car is 0.049 football fields long. They might measure it in feet and inches (14’ 8”), maybe yards (4.9), or–Americans love their cars too!–car-lengths (1). But none of these are football-related!

Perhaps the football itself would be a reasonable measure of length. By NFL standards, a football must be 11 to 11¼ inches long. A 14-foot 8-inch car is 15½ to 16 footballs long. A Big Mac is around a third of a football in diameter.

I think the football has a big problem as a basis for length measurements: it’s just too big to be useful. It’s almost a foot long, and we divide that into inches already. Fractional footballs sounds like an unwieldy unit.

My solution instead draws inspiration from both the football field and the metric system. Football fields are divided into tens: 100 yards long, 10 yards for a first down¹. Metric units are also divided into powers of ten. Meters ($1 = 10^0$), kilometers ($1000 = 10^3$), centimeters ($0.01 = 10^{-2}$), millimeters ($0.001 = 10^{-3}$), even gigameters ($1\ \mathrm{billion} = 10^9$). Let’s divide the football field into 1000.

There are 100 yards in a football field, so we’re looking at a tenth of a yard. Deciyards doesn’t sound very interesting or American though. There are also 10 first downs in a football field. So 1/1000th of a football field is 1/100th of a first down. A centifirstdown. That sounds pretty good to me!

Introducing the Centifirstdown

The centifirstdown should be America’s de facto comparison unit for moderately-sized lengths and distances. One centifirstdown is 3.6 inches, or 9.144 centimeters. A Big Mac is about a centifirstdown in diameter. (Put a hundred Big Macs side-by-side, and you get a first down!) An average “mid-sized” American car is about 50 centifirstdowns long. (Put two cars end-to-end, and you get a first down!)

Because this length is merely intended to be a benchmark for other lengths, it need not be used precisely. You would usually expect lengths to be reported in easy integer numbers of centifirstdowns. Also, you wouldn’t use fractional centifirstdowns, except maybe a half. If something is much smaller, yet another benchmark should be used instead. I’ll leave defining a “small” football-related benchmark as an exercise for the dear reader.

1. Technically, 10 yards from the original line of scrimmage is the distance the ball must progress to achieve a first down–not a first down itself. This abuse of terminology is perfectly understandable and acceptable to most people, so I use it here without further justification. ↩

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