What is Trade Size?

The Contract Size/Traded Units is the measurement of contracts for a given trade.

1 lot = 100,000 units.
0.1 lot = 10,000 units.
0.01 lot = 1000 units. 

What is Forex Leverage and Margin?

The definition of leverage is to have an upper hand. Ratio is on your side.

In a regular trade you would purchase a £10 item with £10. In forex, your leverage allows you purchase that item for a cheaper price with less funds.

A £100 account with a leverage of 1:100 would mean for every £1 you deposit, the broker would give you access to £100. In total, you would have:

£100 (equity) x 100 (leverage) = £10,000 (margin)
£100 (equity) x 500 (leverage) = £50,000 (margin)
£10,000 (equity) x 100 (leverage) = £100,000 (margin)

What is Margin requirement?

Depending on the currency pair, the margin requirement is calculated as follows:

rate x trade size (units) x margin (%) = margin used

For example:

GBPUSD = 1.25000 is £1 per $1.125 as GBP is our account currency. 

£1 x 10,000 units (0.1 lot) x 0.01 (1/leverage) = £100