How To Measure Koi: Understanding Koi Sizing Before You Buy

One of the most common questions we receive from customers is, "How do you measure your koi?" We believe in complete transparency when it comes to the size of the fish we sell, so we'd like to explain exactly how we measure every koi that appears on our website, and advise on how you can measure your own koi at home.

Our Measurement Process

Every koi is measured individually before it is listed for sale. To ensure consistency and accuracy, we use a dedicated 10-gallon measuring tank with an adhesive measuring strip attached to the outside of the tank.

When measuring a koi, we gently position the fish flat against the side of the tank. The koi's mouth is placed directly in the corner of the tank at the zero mark of the measuring strip. This technique took a long time to develop and in that time we’ve found that this method causes the least stress for koi.

We Measure Every Fish

Unlike some sellers who may estimate the sizes of their koi for sale, Every single koi on our website is measured individually and every part of the koi is included in the measurement, which is generally the standard for this industry.

This means that every part of the fish is included in the measurement, including:

The head
The body
The caudal peduncle (tail section)
The full tail fin

Our goal is to provide measurements that accurately represent the fish you will receive.

Important Information About Butterfly Koi

If you're purchasing a Butterfly Koi, it's especially important to understand how measurements are taken.

Butterfly Koi are known for their long, flowing fins and tails. Because we measure the entire fish, including the full length of the tail fin. Butterfly Koi's listed size may include several inches of tail extension.

In some cases, the tail fin of a Butterfly Koi can be nearly as long as, or even longer than, the fish's body itself. For example, a Butterfly Koi listed at 12 inches may have a body length that is 2/3 of the length it is listed at, because part of that measurement comes from the extended tail fin.

This is not an error, it's simply the result of measuring the fish from nose to the very tip of the tail, which is the same method we use for every koi we sell.

This Kikokuryu Butterfly Measures at 9.5”

(While this is an extreme case, not the the tail length makes up for almost half its size.)

Why We Measure This Way

We use a consistent measurement method for every koi because it provides a clear and objective way to compare fish.

Our commitment to accurate sizing helps ensure there are no surprises when your new koi arrives.

If you ever have questions about a specific fish's body length, fin length, or overall appearance, we're always happy to help. Our goal is to provide you with the information you need to purchase with confidence.

Step by Step: How To Measure Koi

The aquarium is filled about two thirds with water. One person holds the fish with two hands against the side just below the ruler while the second person records the measurement. It is important that the person handling the fish is comfortable doing so and uses two hands. The Koi bowl is kept directly beside the measuring tank so the fish can be transferred back and forth quickly and safely. When at all possible we avoid using nets to handle the fish but rather use our hands. The use of nets can strip the fish of its slime coat and allows the fish to flop around and possibly injure itself.