How many albums does a band/group need to seel before they go gold, platinum, diamond and such?

Like, silver, gold, platinum, double platinum, and diamond

It’s different depending on what country you’re talking about. In the United States, for example, the levels are:

Gold = 500,000
Platinum = 1,000,000
Diamond = 10,000,000

Meanwhile in the United Kingdom, its:

Silver = 60,000
Gold = 100,000
Platinum = 300,000

Things like “Double Platinum” are just twice the normal Platinum level–or 2,000,000 in the US.

Gold Diamond Double
Gold Diamond Double
Gold Diamond Double