How many records must be sold to classify an album platinum?

One million (1,000,000)

250,000 If i remember correctly.

According to Wikipedia, gold record certification varies by country. In the United States, an record must sell 500,000 copies to be certified gold. It varies by country but in the United States...

One million

current RIAA criteria 500,000 units: Gold album 1,000,000 units: Platinum album 2,000,000 or more units: Multi-Platinum album 10,000,000 units: Diamond album