The UK stunned the world when voters decided Thursday to leave the European Union. World financial markets reacted violently with the British pound crashing and the stock markets plummeting.

On Friday, the S&P 500 (^GSPC) plunged 75 points or 3.6%. The Dow (^DJI) fell 610 points or 3.4%. The drops in these US stock markets surely had some folks wondering about the US's exposure to the UK.

However, the US economy and stock market doesn't actually have much direct exposure to the UK.

US trade exposure to UK is miniscule

"American exports of goods to the United Kingdom totaled $56 billion last year," Wells Fargo's Jay Bryson observed. "However, this figure pales in comparison to the $218 billion that went to the EU-27, not to mention the $1.5 trillion of total US exports last year."

At just $56 billion, exports to the UK accounted for under 4% of US exports in 2015. That's about 0.4% of US GDP, Bryson noted.

"Even if the UK economy slips into recession, which would depress British demand for American goods, the direct economic impact on the US economy would be miniscule," Bryson said.

US financial exposure to UK is limited

What about America's exposure to British bonds and stocks?

"Direct financial effects on the US economy also appear to be limited," Bryson said. "American bank exposure to British entities (i.e., households, businesses and the government) totals nearly $500 billion, but this amount represents only 3% of total US bank assets. A UK recession could cause some of this exposure to turn to non-performing status, but it likely would not have a meaningful [impact] on the overall American financial system."

Remember, the value of this stuff is unlikely to go to zero. It's also unlikely to lose half its value. All of this is to reiterate how small the exposures are.

"Americans own $1.3 trillion worth of British securities, 70% of which are UK equity securities," Bryson continued. "But with $70 trillion worth of financial assets, household balance sheets in the United States would be little affected by lower prices of British securities, if those prices declines were confined solely to British assets."

US stock market exposure to UK is immaterial

Despite the massive and multi-national nature of America's biggest corporations, the US stock market's direct exposure to the UK is very small.

"According to FactSet Market Aggregates and FactSet Geographic Revenue Exposure data (based on the most recently reported fiscal year data for each company in the index), the aggregate revenue exposure of the S&P 500 to the United Kingdom is 2.9%," FactSet's John Butters wrote. "This is the 3rd highest country-level revenue exposure for the index, trailing only the United States (68.8%) and China (4.9%)."