In the wake of the UK's decision to leave the European Union, Americans can't help but wonder what this means for them.

The US's direct exposure to the UK is actually rather limited. According to data cited by Wells Fargo, the UK accounts for just under 4% of US exports, which represents about 0.4% of US GDP. American bank exposure to British entities totals nearly $500 billion, which is just 3% of total US bank assets. Americans own $1.3 trillion worth of British securities, which is just a tiny fraction of the $70 trillion worth of US household financial assets. And according to data from FactSet, "the aggregate revenue exposure of the S&P 500 to the United Kingdom is 2.9%."

Despite those small direct exposures, the UK still has the potential to do significant damage to the US economy.

The Brexit could hit the US economy via tight financial conditions

While most economists acknowledge the minimal direct exposure, they warn that the uncertainty ignited by the Brexit vote could seep into the US economy in one important way: tighter financial conditions.

Simply put, tighter financial conditions means that it is harder and more expensive for businesses and consumers to get money. That in turn leads to less borrowing, less investing, and ultimately less economic activity. Tighter financial conditions manifest in several ways including volatile stock and bond markets, which is what the world has been experiencing since the Brexit votes were counted late Thursday.

This is a big deal because it's not about whether a business or consumer is exposed to the UK. Rather, it's about whether a business or consumer borrows money or requires investment capital, regardless of exposure to the UK.

"The repercussions will depend crucially on the magnitude of the fall-out in global financial markets," Capital Economics' chief US economist Paul Ashworth said in a note published right after the vote.

"There is a risk that financial turbulence has a real economy impact," Credit Suisse's Ric Deverell warned.

"For most countries outside the EU the bigger impact will most likely be felt on the real economy via financial markets," HSBC's Janet Henry said on Friday. "Volatility and heightened uncertainty will likely be the order of the days and weeks ahead."

Critically, this all has implications for monetary policy. Last week, Federal Reserve Chair Janet Yellen warned of potential fallout from a Brexit scenario.

"One development that could shift investor sentiment is the upcoming referendum in the United Kingdom," Yellen told Congress in her Semiannual Monetary Policy Report. "A UK vote to exit the European Union could have significant economic repercussions. For all of these reasons, the Committee is closely monitoring global economic and financial developments and their implications for domestic economic activity, labor markets, and inflation."