Standard lot

The reference size against which every other volume is expressed. In foreign exchange one convention covers the whole asset class: a standard lot is one hundred thousand units of the base currency, a mini lot a tenth of that, a micro lot a hundredth and a nano lot a thousandth. Outside foreign exchange there is no single convention, because the unit is whatever the instrument is measured in: troy ounces for gold, barrels for oil, a money amount for each index point, a number of shares for a share contract.

Everything downstream of size is computed from it. Notional value is the number of lots multiplied by the contract size and then by the price. The value of one pip is the contract size multiplied by the size of a pip. The margin requirement is a percentage of the notional value, so it moves with volume as well. Volume is therefore the single control that changes cost, financing and the money value of a given price move all at once.

Assuming a lot means one thing is the error. The minimum size and the smallest increment above it are instrument settings stated in the contract specification rather than universal figures, and two instruments quoted at similar prices can carry very different exposure for the same stated volume. A platform's prefilled volume is a default in the interface and carries no meaning beyond that.