What a lot is

The field the ticket asks for first 

On every order ticket there is a small numeric field, usually labelled volume or quantity, sitting between the instrument and the order type. It accepts a number to two decimal places. Nothing printed beside it says what that number counts, and the platform acts on whatever is typed there without asking a second time. It is the control that turns a view about a market into an amount of money that moves, and it is the least explained thing on the screen.

Three things the field is not are worth stating before what it is. It is not the amount of money that will be posted against the position. It is not the amount of money that can be lost. It is not the value of the contract. All three of those are figures derived from it, and each is derived differently. The field itself states a quantity of the underlying, and quantity is the only thing it states.

What one lot contains 

Foreign exchange settled on a single convention long before retail platforms existed, and the convention is a round one. A standard lot is one hundred thousand units of the base currency. It is not a range, it is not a per firm setting, and it does not change with the price of the pair. The word standard is doing real work: it names a quantity the whole market writes contracts in, so a size can be quoted between two parties without either restating what it means.

Two smaller sizes follow from it by simple division. A mini lot is a tenth of a standard lot, so ten thousand units of the base currency. A micro lot is a hundredth of a standard lot, so one thousand units. They are not separate instruments and they are not separate contracts. They are the same contract written in a smaller quantity, which is why the ticket expresses them as decimals of a lot rather than as three different products in a list.

What gets counted, and in which currency 

The units a lot counts are units of the base currency, the one written first in the pair. A standard lot of a euro against dollar contract is one hundred thousand euro. A standard lot of a sterling against yen contract is one hundred thousand pounds. The second currency in the pair is not being counted at all: it is the currency the count is being priced in, and it arrives in the arithmetic only when the unit count is multiplied by the rate.

That multiplication gives the notional value of the contract, which is the figure profit and loss is calculated on. The distinction that matters is which of the two numbers is fixed. The unit count is fixed by the lot convention and stays where it was put. The notional value is not fixed at all, because it is the unit count multiplied by a rate that moves, so the same size entered on the same pair on two different days is the same quantity of the base currency and a different amount of money in the quote currency.

Fractions of a lot, and the sizes a contract permits 

Because the field takes decimals, the sizes between the three named ones are available too, and most sizes traded on retail platforms have no name at all. Fractional sizing is not unlimited, though, and the limits belong to the instrument rather than to the platform. Three of them are published in every contract specification.

• The minimum size, the smallest quantity a contract can be written in. It is not the same figure for every instrument, so an instrument whose minimum is a micro lot sits in the same list as one whose minimum is far larger.
• The step, the increment sizes fall on between the minimum and the maximum. It makes the sizes in between a ladder rather than a continuum, and a size that misses a rung is rejected rather than rounded.
• The maximum a single order may be written in, and separately the maximum an account may hold open at once. They are different limits, and an order can satisfy the first while failing the second.

Why lot size and risk are not the same thing 

A lot number is frequently read as though it were a measure of how much is at stake. It is not, and the reason is that it is one term in a product of three. What a position gains or loses is the quantity it covers, multiplied by the distance the price travels, converted into the currency the account is denominated in. The lot number fixes the first term. It says nothing about the second, and nothing about the third.

The consequence is that two positions entered at an identical lot size can carry entirely different money exposures. Instruments differ in what one increment of their price is worth per unit, and they differ in the currency that value arrives in, so identical quantities produce unequal amounts of money. The arithmetic that turns a quantity into a money value per increment is pip value, and it is the subject of the next lesson. Until it is done, a lot number is a quantity and nothing more.

One relationship does hold cleanly, in both directions equally. Size scales the result linearly: doubling the quantity doubles the money produced by a given move, and it doubles it identically whether the move is favourable or adverse. Since profit and loss are calculated on the full notional value of the contract while only a percentage of that value is posted as margin, a loss is measured against the whole contract rather than against the money posted, so it can exhaust the margin entirely and is not limited to the amount deposited. A favourable move is measured on exactly the same basis.

The second term, the distance a price is allowed to travel before a position is closed, is set by the orders attached to it and not by the size field, which is why later lessons in this module treat the two separately. Nothing on this page assesses what quantity is appropriate in any set of circumstances, and no figure is put forward for any reader.

Where the field appears on the ticket 

A YAL account runs on one of two platforms, MetaTrader 5, and the two present the same quantity in two different notations. On MetaTrader 5the field is labelled volume and is expressed in lots, so a standard lot is entered as one whole unit and a micro lot as a small decimal on that same field.

Only the notation differs, which is the practical reason the conversion above is worth having by heart: a number read in one notation and typed into the other is out by a factor of one hundred thousand, and the ticket has no way of knowing which unit was meant. Both platforms read the minimum, the step and the maximum from the instrument's specification and refuse an entry outside them, which catches impossible sizes and not merely wrong ones.

Where the conventions differ 

The standard lot is a foreign exchange convention, and it is the only asset class where a single number covers everything in it. A lot of an index contract, a metal, an energy or a share is a different quantity of a different thing in each case, stated per instrument rather than per class, and the habit of reading a lot number as a fixed exposure travels badly across that boundary. What one contract covers outside foreign exchange is the subject of the lesson after next, and the figures are not enumerated here.

Practitioners also disagree, in print and at some length, about whether sizing should be reasoned in lots at all. One tradition holds that lot notation is an abstraction that hides the exposure behind a tidy decimal, and that quantity is better reasoned in units or in notional value, where the amount at stake is visible in the number itself. Another holds that the platform's native field is the thing that actually gets filled in, that every mental conversion is a place an error enters, and that the safer discipline is to work in the units the ticket accepts. Both are describing the same failure from opposite ends, and neither position has settled the argument.

The size words themselves are less standardised than they look. Mini and micro are widely used and widely understood, but they are market usage rather than defined terms, some materials simply say a tenth or a hundredth of a lot, and names for sizes below a micro lot appear in trading literature with no single agreed meaning. A size word is therefore only as reliable as the unit count behind it, which is the number the contract is actually written in.