We’ve all been there. You’re standing in the pasture, looking at a gangly, long-legged youngster, completely smitten. Maybe it’s your first foal, or perhaps you’re looking at buying a yearling that has stolen your heart. But as you watch them gallop across the field—legs flying everywhere, looking a bit like a spider on roller skates—one big question pops into your mind.

How big is this horse actually going to get?

Will they grow into those massive knees? Are they going to be a perfect 15-hand trail partner or a 17-hand giant that requires a stepping stool to mount?

Enter the string test. It’s a trick as old as horsemanship itself, passed down in barns from generation to generation. It’s the kind of thing you might see an old cowboy do with a piece of baling twine, or a breeder do with a specialized measuring tape.

The string test is a simple method for estimating a horse’s mature height based on the length of its lower legs. For accuracy, some methods start the measurement at the hairline or coronet band, providing a precise reference poiFnt.

While it sounds a bit like magic—or perhaps an old wives’ tale—there is actually some biological logic behind it. Certain bones, like the cannon bones, are nearly their full length when a foal is born, making early predictions possible. And honestly? It’s just plain fun to do.

Whether you are looking for a pony for your kids or a warmblood for dressage, knowing how to string test a horse is a handy skill to have in your back pocket.

Just remember: while this test is surprisingly reliable for many, it is still an estimate. Think of it as a helpful guide rather than a written guarantee from Mother Nature.

The string test relies on measuring specific points on your horse's leg — the distance from the coronet band (that's where the hoof meets the leg) up to the middle of the knee joint. This measurement, taken in inches, is basically the holy grail for estimating your horse's mature height.

Let me break this down for you the way it was broken down for me... the cannon bones are these long, sturdy bones that run from just below the knee to the fetlock. Whether your horse has long or short cannon bones? Well, that can make all the difference in their final height. Here's what really gets me though (and maybe you'll find this as fascinating as I did)—these cannon bones do most of their growing early in life. By the time your foal is just a few months old, its cannon bones are already close to their full length. That's why the string test works so well... it's surprisingly accurate for predicting how tall your young horse will be at maturity.

When you use the string test, you're measuring from the coronet band up to the middle of the knee. This distance is reliable because (and this is where it gets interesting) as your horse grows, the rest of their body—like the shoulder, barrel, and withers—will catch up to the legs, but the length of the cannon bones stays almost the same. The withers (that's the highest point of the shoulder where the neck meets the back) are where we officially measure a horse's height, which is always given in hands. (One hand equals four inches, in case you're wondering.)

It's one of those methods that's been passed down through generations of horsemen and breeders... and honestly, it's pretty amazing when you think about it. By using a simple string to measure from the ground at the coronet band to the middle of the knee, you can estimate your horse's final height with surprising accuracy—often within an inch or so. This is especially handy if you're breeding (or if you're like me and just can't help but wonder if your foal will grow into a tall, statuesque adult or stay closer to the ground).

Of course, every horse is unique... isn't that the truth! Growth rates can vary depending on breed, genetics, and nutrition. Some horses will reach their mature height by their first birthday; they usually reach their full height by 4 to 5 years old, but actual skeletal maturity, especially the spine, can continue until 6 to 8 years of age.

In the end, understanding your horse's anatomy—especially the length of those all-important cannon bones—makes the string test a reliable and fun way to estimate mature height. Whether you're planning for future tack, training, or just satisfying that curiosity that keeps you up at night... knowing how to measure and interpret these distances gives you a real advantage in understanding your horse's development and care.

Before we run out to the barn with our measuring tapes, let’s chat about why this works. It seems wild that measuring a leg could tell you how tall the withers will eventually be, doesn’t it?

The theory relies on how horses grow. Unlike humans, who grow relatively proportionally over time, horses grow from the ground up. Their lower leg bones—specifically the cannon bone—are some of the first to finish growing. In fact, a foal’s lower legs are almost their full adult length by the time they are yearlings.

Because those lower growth plates fuse and finish their work early, the length of the lower leg serves as a constant. The rest of the horse—the barrel, the shoulder, the depth of girth—catches up later. By using the length of these “finished” bones, we can project the final height of the “unfinished” body.

However, accuracy isn’t perfect. Factors such as nutrition, early gelding (which can cause horses to grow taller), and specific breed traits can skew the numbers. It’s also been observed that geldings often grow slightly taller than stallions with the same genetics. A draft horse grows differently than a Thoroughbred, and a Quarter Horse might surprise you with a late growth spurt. But for a general prediction? Studies and anecdotal evidence have found the string test to be reliable within a certain margin, so it’s often spot on.

There isn’t just one way to solve this puzzle. Depending on who taught you (or which YouTube rabbit hole you went down), you might have seen different variations. Some people learn how to pull the string correctly from a video demonstration, which can help ensure accurate measurement. We are going to cover the two heavy hitters that most horse people rely on.

This is arguably the most popular method, especially for yearlings. It’s interactive and gives you a visual representation of the height right there in the air. This method is great for checking how tall your guy might get as he grows.

The logic here is that the distance from the horse’s elbow to their ergot (that funny little callus on the back of the fetlock) is roughly half of their mature height. Or, more visually, the length of the lower leg is equal to the depth of the body from the elbow up to the withers.

This method is generally most accurate for horses between one and two years old (often called “long yearlings”). At this stage, the legs are long, but the body hasn’t deepened yet.

If you have a very young foal—we’re talking weeks or just a few months old—the elbow-to-ergot test might be tricky because they are so wiggly, and their proportions are drastically different.

For the little ones, some breeders prefer the “Knee to Fetlock” method. The idea is that the length of the cannon bone (measured from the middle of the knee to the fetlock) represents one-quarter of the horse’s final height. By measuring this short distance and multiplying it by four, you get a ballpark figure for their adult size. This method is especially useful for predicting the height of youngsters before they reach maturity.

While less common than the flip test, it’s a great party trick to try if you have a foal on the ground and want to start guessing early!

Ready to give it a try? You don't need fancy equipment—just a little patience and a cooperative horse. Here is exactly how to do the classic "Elbow to Ergot" string test.

You will need a soft measuring tape (the sewing kind works best) or a piece of non-stretchy string or baling twine. If you use a string, you'll also need a regular tape measure to measure the string afterwards.

This is crucial! If your horse is resting a leg or standing downhill, your measurement will be wrong. Lead them to a flat, level surface—like a concrete barn aisle—and ask them to stand square with weight evenly on all four feet.

For the beginner horseman, anatomy terms can be confusing.

Place one end of your string or tape on the point of the elbow. Hold it there securely (you might need a friend to help keep the horse still). Run the string down the leg to the ergot.

Safety Tip: Watch your head! When you are crouching down near a young horse's front legs, stay to the side, not directly in front, in case they strike out or spook.

Now, you have two choices:

The Visual Flip: Keep your finger firmly on the point of the elbow to hold the string in place. Take the bottom end of the string (the part that was at the ergot) and rotate it straight up into the air, vertical to the ground. The point where the string ends in the air is the estimated height of the horse’s withers. You can stand back and see—is it eye-level with you? Is it way over your head?

The Math Variation: Measure the length from the elbow to the ergot in inches. Many horse owners believe this length represents roughly half the final height, or that you can use a conversion chart. For easier interpretation, round your measurement to the nearest quarter inch or hand before comparing or converting. However, the most reliable “math” version of the string test is actually a different calculation often used with the knee-to-coronet measurement, so the “Flip” is usually your best bet for the Elbow-to-Ergot technique.

Alternatively, if you are using Method #2 (Knee to Fetlock) for a foal: Measure from the center of the knee joint down to the center of the fetlock joint. Take that number (say, 15 inches) and multiply by 4. (15 x 4 = 60 inches).

Horses are measured in "hands," where one hand equals 4 inches.
If your measurement resulted in 60 inches:
60 ÷ 4 = 15.
Your horse is estimated to be 15 hands high (15.0 hh).

If you got 61 inches:
61 ÷ 4 = 15 with a remainder of 1.
Your horse is estimated to be 15.1 hands high.

Timing matters. If you try to string test a newborn foal using the flip method, you might get a wonky result because they are basically all leg and no body!

The sweet spot for the Elbow to Ergot test is generally considered to be between 6 months and 18 months of age. This is the “awkward teenager” phase where the legs are established, but the body has a lot of catching up to do. Many breeders swear by doing it at a horse’s first birthday (12 months) for the most consistent results. In fact, many breeders find the string test to be most true when performed around one year of age, as this timing provides a more reliable prediction of mature height.

For very young foals (under 6 months), the Knee to Fetlock x 4 method is often preferred, though it is notoriously more problematic to get an accurate measurement on a wiggly baby.

You also need to consider the breed.

If you search “is the string test accurate for horses” online, you will find forums full of arguments. Some owners say, “It predicted my mare to the exact half-inch!” Others will say, “It said my gelding would be 16.2 and he stopped at 15.1.” Many owners have compared their string test results to their horses' actual adult heights, with mixed outcomes—sometimes the prediction is close, other times it's off by more than an inch. Some people were told by breeders or vets that the string test is a reliable method, while others were told it’s not dependable and should only be used as a rough estimate.

The truth lies somewhere in the middle. The string test is surprisingly accurate—often within an inch or so—for the average light riding horse (like a Quarter Horse or Thoroughbred).

However, it cannot account for:

Think of the accuracy as a “probability,” not a prophecy. It gets you in the right ballpark.

We love the string test because it’s free and easy, but it’s not the only tool in the shed.

To make sure your “guesstimate” is as good as possible, keep these tips in mind. Many of these tips were learned through years of hands-on experience:

Even though it’s simple, it’s easy to mess up. You may have heard some of these mistakes from other horse owners or trainers. Here are a few pitfalls to avoid:

You can, but it won't tell you much! On a mature horse, the "flip" test should essentially confirm their current height. If you flip the string up and it lands exactly at their withers, it proves the horse is done growing. If the string goes way above their withers, your horse might just be oddly proportioned (long-legged with a shallow body).

It is the million-dollar question! Combining the string test with a look at the parents' heights is your best strategy. If the dam is 15hh and the sire is 15hh, and the string test says 16.2hh, take that result with a massive grain of salt.

Yes. Draft breeds often have very deep bodies (the distance from girth to spine), so the leg measurement might slightly underestimate their bulk and height. Conversely, very leggy breeds like Thoroughbreds might test taller.

Yes, because the test relies on the lower growth plates fusing early. If a horse has an issue with growth plate fusion or developmental orthopedic disease, their growth patterns might be irregular.

Not necessarily better, just different. Genetics (parent height) gives you the genetic potential. The string test gives you the physical trajectory based on current skeletal growth. Using both gives you the complete picture.

The string test is one of those traditions in the horse world that has been passed down that bridges the gap between science and folklore.

While it’s not an exact science, it helps you plan for the future. It enables you to decide whether you need to consider buying a bigger trailer or should start doing yoga to help you mount your future giant.

So go ahead—grab a piece of twine and head to the barn. Have fun with it! Just remember that whether your horse ends up being 14.2 or 16.2, the best horse is the one that brings you joy.