With 16.9 million visitors coming to San Francisco and spending more than $9 billion in 2013 (the most recent full year of statistics available), there's no doubt that the San Francisco tourism industry is booming. Who doesn't want to see the Golden Gate Bridge, cable cars and Alcatraz? This means during an average day in San Francisco, 134,231 visitors spent $25.7 million daily (including spending related to meetings and conventions).

But if you're traveling from another country, you have a problem to deal with: Your money isn't in dollars and most San Francisco merchants won't take foreign currency. You have to exchange it. Currency exchange comes with fees; if you're not careful, you could spend far more than you need to. Here's how (and how not) to do it.

Convenience comes at a price. Once you get off of the plane and into the airport, it won't be long before you see a currency exchange window. Some airports now have them at the gates but the fees are higher than other options. You might pay as much as 25% more in fees. They may say something like no fees on their signage but don't be fooled. The fees are probably rolled into the exchange rate. San Francisco International Airport has a currency exchange in the Main G Terminal, but there are probably better options.

Again, it's convenient and it's touristy so it's going to cost you. Many of the major hotels will exchange the more common currency for American dollars, but the exchange rate isn't likely to be favorable. Avoid if you can.

Once you get to the United States it might be too late to use a branch of your own bank. If you do the exchange in your home country before you leave, your bank will likely offer much better rates than U.S. banks – and with lower fees. A couple of weeks before your trip, check with your bank. You might be able to make the exchange on the spot or might have to order the currency. There will be a small delivery fee, but it's probably much less than exchanging in the United States. Keep the amount of cash you take with you to a minimum.

If you need cash and you didn't exchange it in your home country, the ATM is probably your best choice – if you find the right ATMs. Your bank likely partners with some U.S. banks. Find out which ones before you go. If you use a partner ATM, you won't pay the extra fees associated with out-of-network machines. ATM fees along with bank fees can make an ATM withdrawal rather pricey.

Most people agree that other than a little bit of emergency cash to cover places that don't take plastic, your credit card is your best choice. If you have a credit card that doesn't charge a foreign transaction fee, you won't pay exchange fees while on your trip. If your card does charge the fee, consider getting a new one if you frequently travel internationally. Or, just pay it – the fee probably won't be more than 3%, still lower than most other options. (For hints on which card issuers to research, see this story about U.S. based cards: Top Credit Cards With No Foreign Transaction Fee.)

Avoid cash. Not only are there safety risks that come with carrying large amounts of cash, the cost to exchange it for U.S. dollars – then re-exchange back to your home currency – make it a bad deal. Stick with your trusty credit card. And enjoy San Francisco. for more information, see The Best Places To Exchange Currency and How Foreign Transaction Fees Work.