Position sizing on gold: turning lot size into real risk

What a lot means on gold

For most brokers, one standard lot of XAUUSD represents 100 troy ounces. A mini lot is 10 ounces, and a micro lot is 1 ounce. So 0.01 lots — the smallest size most platforms allow — is one ounce of gold.

From that, everything else follows. If gold moves one dollar, a standard lot gains or loses about $100, a mini lot about $10, and a micro lot about $1. The contract size is the only conversion factor you need.

Why gold is not like a currency pair

A currency pair is quoted in units of the quote currency, and a pip is a small, stable fraction of price. Gold moves in dollars, and its daily range is large in absolute terms relative to most FX pairs. This has two consequences.

First, the same lot size carries much more risk on gold than on, say, EURUSD, which is why a position size that feels modest on a currency pair can be aggressive on metals. Second, stop distances that look reasonable in pips on FX translate into much larger dollar swings on gold, so copying a stop distance across instruments without converting is a common and expensive error.

Risk-based sizing, in four steps

The method below sizes the position from the risk you are willing to take and the distance to your stop, rather than from a fixed lot number. It is the standard institutional approach and it generalises to any instrument.

• 1. Decide the money you are willing to lose if the trade hits its stop. Express it in account currency, not percent — $50 is unambiguous, '1%' depends on the account.
• 2. Measure the stop distance in price units. If you enter at 4,100 and place the stop at 4,085, the distance is 15 dollars.
• 3. Convert both to the same units. With a standard lot, a 15-dollar move is 15 x $100 = $1,500. So one lot risks $1,500 on this trade.
• 4. Divide your risk budget by the per-lot risk. $50 divided by $1,500 is 0.033 lots. Round down to the broker's step size, which gives 0.03 lots.

The part people skip: checking the result is allowed

Two constraints can override the calculation, and both should be checked before the order goes in. The first is margin: the required margin must be comfortably below your free margin, and a leveraged position that uses most of your equity will be closed by the broker on a routine fluctuation, not on your analysis.

The second is the broker's volume limits. Many brokers enforce a maximum volume per position that is stricter than the platform's own maximum, and some enforce a maximum total exposure per symbol. If your calculated size exceeds either, you either reduce the size or you accept that your stop distance is too wide for the account.

A worked comparison

Suppose two traders each have $5,000 and each want to risk $50 on a gold trade. The first uses a 15-dollar stop, the second uses a 40-dollar stop. Using the arithmetic above, the first sizes at 0.03 lots and the second at 0.012, rounded down to 0.01. Both risk roughly the same money; their positions differ by a factor of three.

This is the point of risk-based sizing: the position becomes a consequence of the stop, not a decision made separately. Traders who pick a lot size first and a stop second have the relationship backwards, and it shows up as a strategy that behaves differently from its backtest.

Where this connects to backtests

A backtest run at a constant lot size and a live account sized by risk are two different equity curves, even on identical signals. The backtest's drawdown is usually the flattering one, because fixed size does not shrink after losses and does not grow before them.

If you plan to size by risk in practice, the only way to know what the equity curve will look like is to simulate it that way — including the rounding down to the broker's minimum lot, which matters a great deal on small accounts where the calculated size frequently falls below 0.01.