What is a stone in British and Irish horse racing?

Follow British or Irish horse racing for long enough, and you’re bound to hear reference to the number of “stone” a horse carries. Or you’ll see a weight assignment listed as “9-10” or “8-6,” which makes no sense if you’re accustomed to thinking in terms of pounds like the “126” carried by Kentucky Derby (G1) starters.

So what are stones, and what does “9-10” even mean? It’s quite simple, though you’ll have to do some mental gymnastics (or grab a calculator) to convert the answers into something you’ll readily recognize.

Defining a stone is simple—it’s an old British imperial unit, and one stone is 14 pounds. While not commonplace in the United States, stones are still used to measure human body weight in the United Kingdom and Ireland.

Since stones are measured on the same scale as pounds, stones can easily be converted to pounds by multiplying the stones by 14. If a horse carries nine stone in a race, it adds up to 126 pounds. Suddenly the 126-pound assignments for the Kentucky Derby don’t seem so arbitrary!

So what does “9-10” mean? Since a stone is a much larger unit of measurement than a pound, horse racing weights aren’t assigned based on whole stones. If they were, we’d be stuck with a limited number of possible weight assignments—112 pounds, 126 pounds, 140 pounds, etc. So in addition to whole stones, fractions of stones are used, and these are naturally measured in pounds.

So when you see a number like “9-10” as a weight assignment in British or Irish horse racing, remember that the first number (the nine) is the number of stones, and the second number (the 10) is the number of pounds. It’s like measuring height in terms of “six feet, eight inches,” only with units of weight.

A horse carrying “9-10” is carrying nine stone (126 pounds) plus 10 pounds, making the total weight assignment 136 pounds. A horse carrying “8-6” is carrying eight stone (112 pounds) plus six pounds for a total of 118 pounds. The second number in the listing can range from 0 pounds to 13 pounds; just as you would never list your height as “five feet, 12 inches” (which is six feet), you’ll never see a weight assignment of “8-14” (which is nine stone).

Now that you’re up to speed on stone assignments, you can approach British and Irish horse racing without scratching your head over unfamiliar weight assignments. That’s a benefit if you’re handicapping one of those famous British handicaps with 30+ horses and so, so many different weight assignments.