You can buy or sell different amounts of each currency pair - from as low as $1,000 to $500,000 (the maximum position size in the largest account) at any point. One standard lot is equal to $100,000 worth of currency, but you can also enter positions for $10,000 (mini lot) or $1,000 (micro lot) increments. This is automatically calculated on your dashboard here.
To calculate the notional value of your trades, we multiply the number of lots traded by the lot size. For example, if you were to trade 50 standard lots, that would equal $5 million in notional value on your account (50 x $100,000). Likewise, you could trade 25 standard lots and 250 mini lots to trade $5 million in notional value (25 x $100,000 plus 250 x $10,000). You can use the chart below to figure out the value of each lot you are trading.