How big do koi fish grow and how long does it take?

Most koi will achieve 24-26 inches. Koi can be stunted during the first 18 months of growth, but if it is from good stock they can later still grow to 20″. There are tosia and what some call jumbo tosai. A tosai is basically a first year koi. read more

Domestic Koi usually grow 12 to 15 inches, Japanese Koi usually grow 22 to 26 inches in length while Jumbo Koi usually grow 34 to 36 inches in length. But all Koi have indeterminante growth which means they grow throughout their lives, so the longer they live the bigger they get. A big koi is an old koi, just like with many fish and reptiles. read more

Back to our favorite Koi. It appears that depending on their age and under optimum conditions Koi can grow over 2 centimeters (almost an inch) per month or faster, remember there are 2.54 cm in an inch. Check out the growth rates in the following graphs. Just click on the charts to expand them - then click on your browser's back arrow to return. read more

I heard something like "you will see them double in size each of the first 2 years and then 1 inch each year after that" but I am not sure how true that is however the person who said that had at least 4 koi over 2 feet long and has hundred of koi so it may be correct. Obviously there are lots of veriable that will play into this. read more