A big reason multinational companies are beating revenue estimates this quarter is the weaker U.S. dollar. But no one--until now--has quantified that effect. CNBC looked at the 19 Dow components that have reported so far and found a multi-billion-dollar boost to the top line from the decline of the greenback. Of those 19 Dow components--about two-thirds of the Dow--one company, Alcoa, had a negative impact on revenue from currency changes. Two companies--AT&T and Intel--told us that there was no effect. But 14 companies had a positive impact, ranging from a low of 7% to a high of 51%. The average company had a 27% positive currency earnings impact. Revenues from these 19 companies are up $21.5 billion for the quarter. Of that amount, $3.4 billion, or 16% has come from positive currency gains. So far, revenues are running about $9 billion ahead of analyst estimates. So the currency factor explains about 40% of the surprise. It's impossible to know how much this has affected the bottom line. Currency gains at General Electric, the parent of CNBC, explained 26% of its revenue growth. But the company says it's had a "miniscule effect on earnings." GE says that's because costs in the local currency also increase. But that will differ from company to company. For some, analysts say, currency gains flow right through to the bottom line. This is double juice for companies: Not only have foreign sales been stronger, but they get those foreign sales at a better exchange rate, helping the top and bottom lines.