How do I calculate the margin required on hedged positions?

When you decide to hedge a position in one instrument (respectively buying or selling the same amount of that instrument), The full margin will be required for both positions.

Example:

You opened the following orders on you trading account:

1) 0.1 Lot Buy EURUSD on price 1.0170 (Margin Requirement: 101.7 $ )
2) 0.1 Lot Sell EURUSD on price 1.0170 (Margin Requirement : 101.7 $ )

Total Margin Requirement: 203.4 $