25 homers home AND road: Babe Ruth is King.

There have been 23 occurrences of a player hitting at least 25 home runs (HR) both at home and on the road in the same season.  Obviously, each batter hit at least 50 HR.  Babe Ruth did it the most times: four.

Player	Year	Team	HRtot	HRhome	HRroad	HRh-r	Rate H-R	Rate % Dif	AB/HRh	AB/HRr	HR%h	Age	bats	First	Last
Babe Ruth	1920	NYA	54	29	25	4	-3.2	-0.46	7	10.2	54%	25	L	Babe	Ruth
Babe Ruth	1921	NYA	59	32	27	5	-2.5	-0.31	8	10.5	54%	26	L	Babe	Ruth
Babe Ruth	1927	NYA	60	28	32	-4	0	0	9	9	47%	32	L	Babe	Ruth
Babe Ruth	1928	NYA	54	29	25	4	-2	-0.22	9	11	54%	33	L	Babe	Ruth
Jimmie Foxx	1932	PHA	58	31	27	4	-2.1	-0.23	9.1	11.2	53%	25	R	Jimmie	Foxx
Ralph Kiner	1949	PIT	54	29	25	4	-2.3	-0.25	9.1	11.4	54%	27	R	Ralph	Kiner
Mickey Mantle	1956	NYA	52	27	25	2	-0.7	-0.07	9.9	10.6	52%	25	B	Mickey	Mantle
Roger Maris	1961	NYA	61	30	31	-1	-0.7	-0.08	9.3	10	49%	27	L	Roger	Maris
Cecil Fielder	1990	DET	51	25	26	-1	-0.8	-0.07	10.8	11.6	49%	27	R	Cecil	Fielder
Albert Belle	1995	CLE	50	25	25	0	-0.4	-0.04	10.7	11.1	50%	29	R	Albert	Belle
Ken Griffey	1997	SEA	56	27	29	-2	-0.3	-0.03	10.7	11	48%	28	L	Ken	Griffey
Mark McGwire	1997	O-StL	58	30	28	2	-2.2	-0.3	8.3	10.4	52%	34	R	Mark	McGwire
Ken Griffey	1998	SEA	56	30	26	4	-1.7	-0.16	10.5	12.2	54%	29	L	Ken	Griffey
Mark McGwire	1998	SLN	70	38	32	6	-0.8	-0.12	6.9	7.7	54%	35	R	Mark	McGwire
Sammy Sosa	1998	CHN	66	35	31	4	-1.8	-0.2	8.9	10.7	53%	30	R	Sammy	Sosa
Mark McGwire	1999	SLN	65	37	28	9	-2.3	-0.33	7	9.3	57%	36	R	Mark	McGwire
Sammy Sosa	1999	CHN	63	33	30	3	-1.3	-0.14	9.3	10.6	52%	31	R	Sammy	Sosa
Barry Bonds	2001	SFN	73	37	36	1	-0.9	-0.15	6.1	7	51%	37	L	Barry	Bonds
Luis Gonzalez	2001	ARI	57	26	31	-5	1.7	0.15	11.6	9.9	46%	34	L	Luis	Gonzalez
Alex Rodriguez	2001	TEX	52	26	26	0	-0.3	-0.03	12	12.3	50%	26	R	Alex	Rodriguez
Sammy Sosa	2001	CHN	64	34	30	4	-1.6	-0.19	8.3	9.9	53%	33	R	Sammy	Sosa
Ryan Howard	2006	PHI	58	29	29	0	-0.6	-0.06	9.7	10.3	50%	27	L	Ryan	Howard
Alex Rodriguez	2007	NYA	54	26	28	-2	0.8	0.07	11.2	10.4	48%	32	R	Alex	Rodriguez
		max	73	38	36	9	1.7	0.15	12	12.3	0.57	37
		min	50	25	25	-5	-3.2	0	6.1	7	0.46	25

Sammy Sosa and Mark McGwire did it three times.  Twice each for Ken Griffey and Alex Rodriguez.

Three players hit the same number home and road:
Albert Belle 1995: 25/25
Alex Rodriguez 2001: 26/26
Ryan Howard 2006: 29/29

In 2001 Barry Bonds hit the most HR: 73; also the most on the road: 36.  Mark McGwire in 1998 hit the most at home for this group: 38; the only player with more at home was Hank Greenberg: 39 in 1938 but only 19 on the road so Hank is not part of this group.

Runners up with 32 road HR:
Ruth 1927; 60
McGwire 1998; 70
David Ortiz 2006, but only 22 at home; 54.

Cecil Fielder (51) and Albert Belle (50) had the minimum 25 HR at home.

Minimum 25 HR on the road:
Babe Ruth 1920; 54
Babe Ruth 1928; 54
Ralph Kiner 1949; 54
Mickey Mantle 1956; 52
Albert Belle 1995; 50

Six times a batter in this group hit more HR on the road:
Babe Ruth 1927: 28/32; 60
Roger Maris 1961: 30/31; 61
Cecil Fielder 1990: 25/26; 51
Ken Griffey 1997: 27/29; 56
Luis Gonzalez 2001: 26/31; 57
Alex Rodriguez 2007: 26/28; 54

Three of the six played their home games in Yankee Stadium.

In this study group the only batter with a better HR rate (AB/HR, lower is better) on the road:

Player

Year

Team

HRtot

HRhome

HRroad

HRh-r

Rate H-R

Rate % Dif

AB/HRh

AB/HRr

HR%h

Luis Gonzalez

2001

ARI

57

26

31

-5

1.7

0.15

11.6

9.9

46%

In this group Gonzalez also had the biggest split (5 HR) and lowest percent of HR at home (46%).

Biggest home plus:
Mark McGwire 1999: 37-28=9; 65.  Also highest percent of HR at home (57%).

The two largest home minus road HR rate differences and also the closest:

Player	Year	Team	HRtot	HRhome	HRroad	HRh-r	Rate H-R
Babe Ruth	1920	NYA	54	29	25	4	-3.2
Babe Ruth	1921	NYA	59	32	27	5	-2.5
Babe Ruth	1927	NYA	60	28	32	-4	0

The Babe played his home games in the Polo Grounds 1920-1922 before the Yankees moved to the House that Ruth Built: Yankee Stadium.  Ruth probably would have hit more HR had the Yankees continued to play their home games in the Polo Grounds but the Giants owned the park and resented the Yanks out drawing them when Ruth brought his HR act to New York from Boston in 1920.

Ironically, the best and worst HR rates for this group were both in 2001 and both home and road for the same players:
AB/HRh AB/HRr
6.1 7    Bonds 2001; 73
12 12.3    Rodriguez 2001; 52

Bonds, of course, has the best rates for any batter ever.

Finally, age was determined simply by subtracting birth year from batting year:
Mantle 25 in 1956, born October 20, 1931 so Mick was actually 24 and younger than Ruth
Ruth 25 in 1920, born February 6, 1895
Bonds 37 in 2001; born July 24, 1964