size of baseball and strike zone

Yes, the ball is slightly smaller.

The strike zone, according to the rule book, is the same. It's how the umpires call it that may differ. But this all depends on the umpire, not the league the umpire represents.

Baseball specifications were posted to this thread a couple of years ago.

In short:

1. The ball must be made of cork, cow hide, and other materials.
2. The ball must be between 141.7 and 148.8 grams.
3. The ball must be between 22.9 to 23.5 cm in circumference.

Can you provide similar specs for MLB baseballs?

The ball is the same size.

     Weight L   Weight H  Circumference L Circumfrence H
MLB  5     oz   5.25  oz      9 in            9.25 in
NPB  5.002 oz	5.253 oz      9 in            9.29 in

Japan tends to call a slightly smaller strike zone than in the U.S. American umpires will frequently give the pitcher a good 2-4 inches (5-10 cm) of the corners. In recent years, more Japanese umpires are giving a little more of the corners (from games I've seen).

Both countries are about the same in not calling anything above the belt.

MLB umpires are now working both leagues while NPB umpires still stick to one league (correct me if I'm wrong).

Japan is also a little more generous with check-swings than in the U.S. In Japan you have to go a little farther past a half-swing to get it called a strike.

(Interesting side note: in the 1960s, MLB check swings got away with much worse - as long as they brought the bat back it was called a check swing.)

[Old thread revival.]

It has been brought up lately because of so many comparisons of Japanese pitchers and thier records once playing in MLB. I have heard, but cannot substantiate that the NPB ball is smaller. Most posts to this question have the NPB and MLB ball just about at the same specs., with an acceptable variance of 1/4 inch from 9 inch circumferance. Does anyone know for sure what the spec. is?

I was told by a MLB scout the ball is smaller in Japan and that the size of the pitchers hands is a major factor when looking at a Japanese prospect.

Before the 2011 season that was the case. However, the biggest change introduced prior to the 2011 season (other than time limits due to the loss of the Fukushima Dai-Ichi Nuclear Power Plant) was moving to the internationally unified ball.

During the spring a year ago there were many pitchers complaining about the increase in size. However, it didn't take them long to learn how to use the new ball and 2011 was far and away the year of the pitcher. For all of their griping during spring, the pitchers showed that they could adjust to the new ball much better than hitters (with but a couple of exceptions) did.

Was this a factor when looking at prospects? Yes. But that part of the equation has now been taken out.