I'm going to go with Basketball-Reference.com and consider the first "NBA" season to be 1946-47.
Here is the raw (unadjusted) ranking of franchises by # of NBA titles won:
17 - Celtics
16 - Lakers
6 - Bulls
5 - Spurs
3 - Sixers/Nationals, Pistons, Warriors, Heat
2 - Knicks, Rockets
1 - Bullets/Wizards, Hawks, Sonics/Thunder, Blazers, Bucks, Mavs, Kings/Royals, Baltimore Bullets*
0 - everyone else
(* The Baltimore Bullets existed from the season ending in '48 to the season ending in '54. They folded, but did win a title in '48.)
Here's a history of the # of teams in the NBA by season (listed by the ending year of the seasons):
1947 = 11 teams [Including Celts, Knicks, Warriors]
1948 = 8
1949 =12 [Royals (Kings), Lakers, Pistons joined]
1950 = 17 [Hawks, Nationals (Sixers) joined]
1951 = 11
1952-53 = 10
1954 = 9
1955-61 = 8 [All 8 are still in the NBA: Celts, Knicks, Warriors, Nationals (Sixers), Pistons, Hawks, Royals (Kings), Lakers.]
1962-66 =9 [Bullets joined]
1967 =10 [Bulls]
1968 = 12 [Rockets, Sonics (Thunder)]
1969-70 = 14 [Bucks, Suns]
1971-74 = 17 [Blazers, Braves (Clips), Cavs] NBA went to 4 divisions, Eastern & Western Conferences for season ending '71
1975-76 = 18 [Jazz]
1977-80 = 22 [SPURS, Nuggets, Pacers, Nets] ABA merger
1981-88 = 23 [Mavs]
1989 = 25 [Heat, Hornets (Pelicans)]
1990-95 = 27 [Magic, T'wolves]
1996-2003 = 29 [Grizz, Raptors]
2004-present = 30 [Bobcats (about to be Hornets again)]
THEORY: It's much harder to win an NBA title in a league with 30 teams and a Finals in June than an league with 8 or 9 or 10 teams and the Finals in freaking April.
I propose that an NBA Title won in year Y is worth T[Y]/30, where T[Y] = # of teams in the NBA in year Y.
In other words, any team winning an NBA title from 1955 thru 1961 gets 8/30 for each title won. Any team winning an NBA title from 2004 to now gets 30/30 for each title won.
Here are the revised standings of adjusted NBA titles:
11.20 = Lakers
7.90 = Celtics
5.60 = Bulls
4.93 = Spurs
3.00 = Heat
2.73 = Pistons
1.80 = Rockets
1.37 = Nationals/Sixers
1.23 = Warriors
1.03 = Knicks
1.00 = Mavs
0.73 = Bullets/Wizards, Sonics/Thunder, Blazers
0.57 = Bucks
0.37 = Royals/Kings
0.27 = Hawks, Baltimore Bullets*
BOTTOM LINE: The Celtics amassed a lot of cheap titles early in the NBA. All things considered, the Lakers should really be considered the NBA standard all time, with the Spurs and Bulls just 3 modern titles away from overtaking the Celts.
Here is the raw (unadjusted) ranking of franchises by # of NBA titles won:
17 - Celtics
16 - Lakers
6 - Bulls
5 - Spurs
3 - Sixers/Nationals, Pistons, Warriors, Heat
2 - Knicks, Rockets
1 - Bullets/Wizards, Hawks, Sonics/Thunder, Blazers, Bucks, Mavs, Kings/Royals, Baltimore Bullets*
0 - everyone else
(* The Baltimore Bullets existed from the season ending in '48 to the season ending in '54. They folded, but did win a title in '48.)
Here's a history of the # of teams in the NBA by season (listed by the ending year of the seasons):
1947 = 11 teams [Including Celts, Knicks, Warriors]
1948 = 8
1949 =12 [Royals (Kings), Lakers, Pistons joined]
1950 = 17 [Hawks, Nationals (Sixers) joined]
1951 = 11
1952-53 = 10
1954 = 9
1955-61 = 8 [All 8 are still in the NBA: Celts, Knicks, Warriors, Nationals (Sixers), Pistons, Hawks, Royals (Kings), Lakers.]
1962-66 =9 [Bullets joined]
1967 =10 [Bulls]
1968 = 12 [Rockets, Sonics (Thunder)]
1969-70 = 14 [Bucks, Suns]
1971-74 = 17 [Blazers, Braves (Clips), Cavs] NBA went to 4 divisions, Eastern & Western Conferences for season ending '71
1975-76 = 18 [Jazz]
1977-80 = 22 [SPURS, Nuggets, Pacers, Nets] ABA merger
1981-88 = 23 [Mavs]
1989 = 25 [Heat, Hornets (Pelicans)]
1990-95 = 27 [Magic, T'wolves]
1996-2003 = 29 [Grizz, Raptors]
2004-present = 30 [Bobcats (about to be Hornets again)]
THEORY: It's much harder to win an NBA title in a league with 30 teams and a Finals in June than an league with 8 or 9 or 10 teams and the Finals in freaking April.
I propose that an NBA Title won in year Y is worth T[Y]/30, where T[Y] = # of teams in the NBA in year Y.
In other words, any team winning an NBA title from 1955 thru 1961 gets 8/30 for each title won. Any team winning an NBA title from 2004 to now gets 30/30 for each title won.
Here are the revised standings of adjusted NBA titles:
11.20 = Lakers
7.90 = Celtics
5.60 = Bulls
4.93 = Spurs
3.00 = Heat
2.73 = Pistons
1.80 = Rockets
1.37 = Nationals/Sixers
1.23 = Warriors
1.03 = Knicks
1.00 = Mavs
0.73 = Bullets/Wizards, Sonics/Thunder, Blazers
0.57 = Bucks
0.37 = Royals/Kings
0.27 = Hawks, Baltimore Bullets*
BOTTOM LINE: The Celtics amassed a lot of cheap titles early in the NBA. All things considered, the Lakers should really be considered the NBA standard all time, with the Spurs and Bulls just 3 modern titles away from overtaking the Celts.