Each symbol is charged a different commission; some symbols, like indices, have no commission. Maybe your broker charges a flat commission rate.
If you cannot find the information on the broker's website, contact them directly for the symbol you wish to trade.
If you trade 1 lot then the commission could be $6, and 2 lots would be $12
Normally you would trade 0.01 lots, so the actual commission is so low you will not notice much difference.
