Depends on what multiplier he uses and what point in the series he uses it, as he always gets stronger.
It is 16,000 when he uses Kaio Ken x2 in the Saiyan Saga. He used up to Kaio Ken x4 in the Saiyan Saga and his max at that point was 32,000. The last time Goku officially used Kaio Ken in Dragon Ball Z, his max power at Kaio Ken x20 was 60 Million. He was equal to Frieza, who was holding back. Goku's power as a Super Saiyan was 150 Million, so a decent gap compared to him at Kaio Ken x20.