[B]I have 7 month old newfoundland dog and I want to know what will be his adault hight.
He is now tall 26.5"(67.5 cm).
i am interested becouse averadge should be 28" but every newfoundland that I have seen was 30" or higher.
Thanks.

The best indication of a dogs' size is going to be the parents. Look at them and you'll get a good idea of how large your dog will be. The breed club sets standards for each dog, so they'll show you the accepted size range for the breed. It's not unusual, of course, for some dogs to be out of standard, either larger or smaller.

My guess is depending on what you have been feeding him, he will be close to the 28''. My puppies continue to grow after 7 months, but very slowly. For the last 4, I have noticed more difference since being given an older dog. My 9 Month old Holly is still a hair shorter than Aster. Late this year, I expect her to be about an inch taller. Slow growth continues into their second year.

The above is only my personal experience. It may be skewed by switching the puppies to an adult chow at 4 months. The dog guide school does that because it slows growth giving more time to develop the sturdy joints a dog needs for a long, active life. If you still have him on a puppy chow, I would pick up some adult chow and work it in until he is eating all adult chow when you finish the puppy chow.

Yes, dogs don't read breed standards or descriptions, and may or may not conform to them.