According to the Bank for International Settlements, the preliminary global results from the 2016 Triennial Central Bank Survey of Foreign Exchange and OTC Derivatives Markets Activity show that trading in foreign exchange markets averaged $5.09 trillion per day in April 2016. This is down from $5.4 trillion in April 2013 but up from $4.0 trillion in April 2010. Measured by value, foreign exchange swaps were traded more than any other instrument in April 2016, at $2.4 trillion per day, followed by spot trading at $1.7 trillion.
The need to exchange currencies is the primary reason why the forex market is the largest, most liquid financial market in the world. It dwarfs other markets in size, even the stock market, with an average traded value of around U.S. $2,000 billion per day. (The total volume changes all the time, but as of August 2012, the Bank for International Settlements (BIS) reported that the forex market traded in excess of U.S. $4.9 trillion per day.)