On average how fast do koi's grow?

There are a lot of things that can affect how fast they grow, water temp, food-quality and quantity, the fish itself. I have had koi that grew an inch a month during the summer months and I have had koi that grew an inch over the entire summer, somewhere in there must be the average.

koi grow alot faster then goldfish do,im not
exacly sure but koi grow fast enough and make great pets.
id say at the end of the summer if you got a koi
if he was about 4 inchs he would be 8 maby even 12 but this
all depends on the space you give him.

bigjk what is the ideal water temp for koi?

most people leave their kois in pond so there is no really ideal temp.
i thinks its actually good to let them go through the four the seasons
although you may be tempted to increase the temp. so that
they will eat more and grow faster.

and about the growth of kois, 4-5 in is not uncommon
any more and its a bonus

Ideal temp for growing is between 65 and 75. But if you live in a region that has a colder winter it is best to let the koi spend the winter below 55 because the Japanese breeders believe that helps the koi live longer lives, but 65 to 75 are the best temps for koi growing.

Like SLS mentioned it is a good idea too let them go through 4 seasons as long as they are not extreme. If you can't keep the water above 45 it would be a good idea too bring them in for the winter. I think as an ideal it would be best too never let it get below 55.
They prefer water in the 72-78 range and this is where you will see the best growth.
Regarding growth rates, there are too many variables. If the koi has good genetics, good water, good food, and plenty of space they can easily grow to 2' long by the time they are 2. And being a female don't hurt. And as a rule, the smaller the fish the faster it will grow.
For instance, my kohaku has gone from 4" to 18" in 11 months. It is going too be a lot harder for this fish too go from 18" to 24" than it was from 4" to 18".

one thing i liked to know
is if its normal for the koi to get fat around the stomach before
a growth spurt occurs
the koi i had was fat in spring and then it grew a few inches in summer(had a streamline body shape)
and now thats its autumn, it is looking fat again
whats going on???

All of my Koi were 2 inches or so last May. I now have 3 that are between 12 and 14 inches and the rest of them are around 10. Give them ideal conditions and they grow very fast.

Where do you guys buy your kois ? The ones I see in petsmart are small (3-5) and are expected to grow at most 24 inches. But I thought kois get larger than that.

thanks for the info everyone
What food do u guys recommend feeding a koi that is about 2-3 inches long?

you can always take normal flake food and soak
it before feeding.Or pellets.

i find that they dont really like flake food
many people feed them pellet food
especially when they get 10 in +
its a good idea also to get bigger pellets
when you fish get bigger

I feed my koi pellets, both the large and small koi, you sould be able to get koi pellets at the pet store. As for where to buy koi, it has been my experience that Koi from Petsmart grow really fast at quickly and then taper off and start to grow slowly, and the more expencive Koi grow kind of slow but stay that pace until they are large. I just bought four more Koi two days ago from aquariumfish.net and they will be delivered later this week, the fish from there have always been high quality for a good price.

Anyone been succesfull using natural foods vegies...etc???

I throw in some cooked corn and lettuce every one in a while, and one a week I throw in an earth worm from the garden for each of the koi and they love the worms.