Baseball Statistics: Isolated Power

Invented by Baseball Prospectus, Isolated Power, abbreviated as ISO, is a measure of a hitter's raw power, in terms of extra bases per AB.

Calculating ISO

According to Baseball Prospectus, Isolated Power is calculated as:

ISO = (2B + (3B*2) + (HR*3)) / AB

So how do we use it? Isolated power is a convenient tool for measuring how well a player is at hitting for power. Using ISO, you can answer such questions as, who was the best power hitter in 2008, or, who is the best power hitter of all time?

Example ISO calculations

If we were tying to determine the best power hitter of 2008, some of the names on the shortlist would have to be:

Alex Rodriguez 2008 ISO

(33 + (0*2) + (35*3)) / 510 = .271

Carlos Quentin 2008 ISO

(26 + (1*2) + (36*3)) / 480 = .283

Manny Ramirez 2008 ISO

(36 + (1*2) + (37*3)) / 552 = .270

Albert Pujols 2008 ISO

(44 + (0*2) + (37*3)) / 524 = .295

Lance Berkman 2008 ISO

(46 + (4*2) + (29*3)) / 554 = .255

Ryan Howard 2008 ISO

(26 + (4*2) + (48*3)) / 610 = .292

Perhaps as no surprise, using ISO, Albert Pujols was the best pure power hitter in 2008.

Top 10 Isolated Power of 2008

1. STL - Albert Pujols - .295

2. STL - Ryan Ludwick - .292

3. PHI - Ryan Howard - .292

4. CHW - Carlos Quentin - .283

5. CIN - Adam Dunn - .277

6. NYY - Alex Rodriguez - .271

7. LAD - Manny Ramirez - .270

8. MIL - Ryan Braun - .268

9. FLA - Mike Jacobs - .266

10. TBR - Evan Longoria - .259

Top 10 Isolated Power Per Season

American League

1. Babe Ruth - .472 - 1920

2. Babe Ruth - .469 - 1921

3. Mark McGwire - .418 - 1996

4. Babe Ruth - .417 - 1927

5. Mark McGwire - .410 - 1995

6. Lou Gehrig - .392 - 1927

7. Babe Ruth - .386 - 1928

8. Jimmie Foxx - .385 - 1932

9. Frank Thomas - .376 - 1994

10. Albert Belle - .374 - 1995

National League

1. Barry Bonds - .536 - 2001

2. Mark McGwire - .454 - 1998

3. Barry Bonds - .450 - 2004

4. Barry Bonds - .429 - 2002

5. Mark McGwire - .418 - 1999

6. Sammy Sosa - .409 - 2001

7. Barry Bonds - .408 - 2003

8. Jeff Bagwell - .383 - 1994

9. Barry Bonds - .381 - 2000

10. Hack Wilson - .368 - 1930

Top 10 Isolated Power of All Time

1. Babe Ruth - .348

2. Mark McGwire - .325

3. Barry Bonds - .309

4. Lou Gehrig - .292

5. Hank Greenberg - .292

6. Albert Pujols - .289

7. Ted Williams - .289

8. Jimmie Foxx - .284

9. Jim Thome - .282

10. Manny Ramirez - .279

As you can see, using ISO, we have determined that Babe Ruth is the best pure power hitter of all time and that Albert Pujols was the best power hitter in 2008.

Isolated Power statistics taken from http://www.fangraphs.com/leaders.aspx?pos=all&stats=bat&lg=all&qual=y&type=1&season=2008&month=0