Gold and Platinum...
  The table below is based on the official RIAA (Recording Industry Association of America) awards, and is probably as accurate as you can get, but it must be borne in mind that any sales figure is open to question - it's not unknown for record companies to sometimes understate sales figures (knowingly or not), the germane example here being Pet Sounds, which is generally regarded as having sold enough to go gold some time in summer 1967. Capitol's reasoning and motives can only be guessed at. One thing must be borne in mind at all times: the record company must request (and pay for) a certification - they aren't awarded automatically.
 
  The current RIAA certification levels are 500,000 units for gold and 1,000,000 units for platinum for singles, and the same figures for albums with additional dollar sales of at least $1 million and $2 million, based on one-third of the list price (although for multi-dics sets, each disc counts towards the award and the dollar sales are not a factor). However, to quote the RIAA, "catalog product, specifically pre-1972 album releases, are eligible for certification by meeting either the unit shipment or manufacturer's dollar requirement for each award level." Translated into English, this means that from 1958-75, the gold qualification for albums was sales of $1,000,000, whereas for a single it was one million units sold. In 1975, the criteria for albums was amended to $1 million in sales at a minimum of 500,000 units sold. The following year the platinum level was introduced, albums being $2 million at 1,000,000 copies, and a straight 2 million copies sold for singles. In 1989 the level for gold singles was reduced to 500,000 copies.  Therefore, although certified gold by the criteria then in place, Endless Summer and "Good Vibrations" would be at least platinum records today (that Endless Summer was on the charts for over three years and only rates gold beggars belief...).
 
The current criteria for DVD/video certification is 50,000 units for gold, 100,000 for platinum.
 
British awards: In the UK, surprisingly, officially ratified awards have only existed since 1973. Before then, from 1959 to 1973 the British music paper Disc awarded silver discs (for sales of 250,000) and gold discs (for sales of 1,000,000): this applied to both singles and albums. The totals were based on information supplied by the various labels, and prior to 1973, only "Good Vibrations" (12/3/66) and "Sloop John B" (1/7/67) were awarded a silver disc. In 1973, the British Phonographic Industry took over. Less surprisingly, the award levels are somewhat lower than the US, being for singles 400,000 (gold) & 600,000 (platinum), and album being 100,000 (gold) and 300,000 (platinum), Additionally theres a lower award, silver, at 200,000 & 60,000 sales respectively. the UK awards are distinguisehed by a different colored background.
 
The digital age: The rise of both digital sales and, more recently and much more importantly, digital streaming has of necessity seen a refining of the various qualification rules. While the basic levels remain unchanged, the method of arriving at the sales figures is more complex these days. In the US, ten digital track sales or 1,500 song streams from an album are treated as equivalent to one purchase of the album. In the UK... I'll be honest, I've read the Official Chart Company rules and I'm confused, but I think it goes like this: 100 paid streams or 600 free streams equals one sale. That's for singles. Albums ? Not a clue.
 
Addendum 10/3/03 - Endless Summer  was certified as triple platinum in late September. And about time too...
 
Award date
Level Title
2/18/65
  Gold   All Summer Long
  Beach Boys Concert
10/1/65
  Gold   The Beach Boys Today
11/15/65
  Gold   Surfin' U.S.A.
  Surfer Girl
2/7/66
  Gold   Summer Days (And Summer Nights !!)
12/21/66
  Gold   Little Deuce Coupe
  Shut Down, Volume 2
  Good Vibrations/Let's Go Away For A While
4/12/67
  Gold   Best Of The Beach Boys
8/14/74
  Gold   Endless Summer
10/4/74
  Gold   The Beach Boys In Concert [2LP]
4/30/75
  Gold   Spirit Of America [2LP]
7/1/76
  Silver
  Gold
  20 Golden Greats
  20 Golden Greats
8/1/76
  Platinum   20 Golden Greats
9/1/76
  Gold   15 Big Ones
12/10/76
  Gold   Best Of The Beach Boys, Volume 2
1/1/78
  Silver   Holland
  15 Big Ones
2/22/82
  Gold   I Get Around/Don't Worry, Baby
4/6/82
  Gold   The Beach Boys' Christmas Album
7/25/83
  Silver
  Gold
  The Very Best Of The Beach Boys Vol. 1 & 2
  The Very Best Of The Beach Boys Vol. 1 & 2
9/7/83
  Platinum   The Very Best Of The Beach Boys Vol. 1 & 2
5/26/88
  Gold   Made In USA [2LP]
1/10/89
  Gold
  Platinum
  Kokomo/other artist B side
  Kokomo/other artist B side
11/27/89
  Gold   Still Cruisin'
8/2/90
  Silver
  Gold
  Summer Dreams
  Summer Dreams
9/1/90
  Platinum   Summer Dreams
12/2/91
  Platinum
  Platinum x2
  Best Of The Beach Boys
  Best Of The Beach Boys
2/5/92
  Platinum
  Platinum
  Platinum x2
  Little Deuce Coupe
  Best Of The Beach Boys, Volume 2
  Best Of The Beach Boys, Volume 2
11/2/93
  Gold   Good Vibrations - 30 Years Of the Beach Boys* [5CD]
6/1/95
  Silver   Best Of The Beach Boys [2CD ]
4/27/99
  Gold
  Platinum
  Platinum x2
  20 Good Vibrations - The Greatest Hits
  20 Good Vibrations - The Greatest Hits
  20 Good Vibrations - The Greatest Hits
2/11/00
  Gold   Pet Sounds
4/6/00
  Platinum   Pet Sounds
11/9/01
  Silver   Very Best Of The Beach Boys**
10/25/02
  Gold   Very Best Of The Beach Boys**
9/4/03
  Gold   Sounds Of Summer - The Very Best Of The Beach Boys
9/30/03
  Platinum
  Platinum x2
  Platinum x3
  Platinum
  Platinum x2
  Platinum
  Endless Summer
  Endless Summer
  Endless Summer
  Made In USA
  Made In USA
  Still Cruisin'
5/6/04
  Platinum   Sounds Of Summer - The Very Best Of The Beach Boys
10/01/04
  Silver   Brian Wilson Presents Smile
11/19/04
  Gold   Brian Wilson Presents Smile
6/10/05
  Silver   The Platinum Collection [3CD]
7/11/05
  Gold
  Platinum
  Brian Wilson Presents Smile [DVD]
  Brian Wilson Presents Smile [DVD]
11/4/05
  Platinum x2   Sounds Of Summer - The Very Best Of The Beach Boys
12/02/05
  Platinum   Very Best Of The Beach Boys**
1/17/08
  Gold   Good Timin' - Live at Knebworth 1980 [DVD]
5/11/12
  Platinum x3   Sounds Of Summer - The Very Best Of The Beach Boys
7/22/13
  Platinum
  Silver
  Silver
  Silver
  Silver
  Silver
  Pet Sounds
  Sounds of Summer
  20 Great Love Songs
  Greatest Hits [1998]
  Hits of The Beach Boys
  I Love You
4/17/15
  Platinum x2   Very Best Of The Beach Boys**
3/30/16
  Platinum   Good Vibrations/Let's Go Away For A While
12/23/16
  Silver   Endless Summer
4/7/17
  Silver   Good Vibrations#
4/21/17
  Silver   God Only Knows#
5/18/18
  Silver   Wouldn't It Be Nice#
11/29/19
  Silver   The Beach Boys with The Royal Philharmonic Orchestra
12/27/19
  Gold   Good Vibrations#
4/24/20
  Gold   God Only Knows#
5/15/20
  Silver   Surfin' USA#
7/17/20
  Silver   I Get Around#
9/11/20
  Platinum x2   Pet Sounds
11/20/20
  Gold   Wouldn't It Be Nice#
1/1/21 
  Silver   Little St. Nick#
7/23/21 
  Gold   Endless Summer
4/1/22 
  Platinum   Good Vibrations#
8/12/22 
  Platinum   God Only Knows#
2/3/23 
  Silver   Kokomo#
11/24/23 
  Platinum   Wouldn't It Be Nice#
x
*
 
**
#
  As noted above, to reach gold certification, this 5CD set had to sell 100,000 units -
  which it did in something under five months. Impressive.
  Not the same collection as the 1983 LPs.
  No, I don't understand this either. The best assumption is that it's a result of
  streaming and downloads.