Working out position size

Most beginners pick a lot size because it looks familiar. A standard lot is 100,000 units of the base currency. On USD/ZAR, one pip is usually worth about R10 per standard lot at an exchange rate near 18.4100. That R10 figure is not fixed. It changes when the rand moves against the dollar, and it varies between brokers because contract sizes differ. So the pip value is the number you should check, not assume.

The order is risk in rand, then stop distance in pips, then pip value. If you start with the lot size, you are choosing the risk by accident. A 0.50 lot on USD/ZAR with a 40-pip stop risks about R200. The same lot with a 10-pip stop risks about R50. The lot size stayed the same, but the risk changed by a factor of four. That is why the stop must come before the size.

The stop distance is not a number you invent. You read it from the chart. If price is at 18.4100 and your stop sits at 18.3800, the distance is 300 pips. That is 0.0300 in rand terms, which is 300 pips because one pip on USD/ZAR is 0.0001. Write the stop level down before you calculate anything. A stop placed after the calculation is a stop placed to fit the size, which defeats the purpose.

Not every risk amount divides neatly by the stop distance. Suppose you will risk R250 and the stop is 60 pips away. R250 divided by 60 is R4.1666 per pip. That is not a round number. You then divide by the pip value. At R10 per pip per standard lot, R4.1666 divided by R10 gives 0.4166 lots. Most brokers round to 0.01, so you would enter 0.41 or 0.42 lots. Rounding down keeps you inside your risk. Rounding up takes you slightly over it.

The rounding matters more on small accounts. If your calculated size is 0.004 lots, a broker that only allows 0.01 lots will not accept it. You then have two choices. You can widen the stop so the same risk buys a larger position, or you can reduce the risk in rand. What you must not do is enter 0.01 lots and keep the original stop. That silently increases the money at risk. The calculation told you the truth. Ignoring it is a choice.

Pip value also shifts while the trade is open. If USD/ZAR moves from 18.4100 to 18.6000, the rand value of one pip changes because the quote currency is the rand itself. For a USD/ZAR position, the pip value in rand is roughly fixed by the contract size, but the value in your account currency can still vary if your account is denominated in dollars. Check whether your account is in rand or in dollars before you trust the R10 figure. If it is in dollars, the conversion adds a step.

Position size is only one part of what a trade costs. The spread is the difference between the buy price and the sell price. On USD/ZAR that spread might be 10 pips or more, and it varies between brokers and between times of day. If your stop is 20 pips away and the spread is 10 pips, you are paying half your stop distance before the market moves at all. The calculation above does not include the spread. Add it to your stop distance when you judge whether a trade is worth taking.

Commission is the other cost. Some brokers charge a separate fee per lot instead of widening the spread. Others build the cost into the spread and charge nothing extra. There is no single rule. You have to read the contract specifications for the account you are using. A broker that charges R70 per standard lot round turn adds R70 to the cost of a 1.00 lot trade. On a 0.10 lot trade that is R7. The smaller your position, the smaller the commission, but the spread cost as a proportion of your risk does not shrink.

None of this tells you whether the trade will work. Position size controls how much you lose if the stop is hit. It does not control how often the stop is hit. A correctly sized trade can still lose. The purpose of the calculation is to make the loss small enough that you can take the next trade without needing to win it back immediately. That is the whole benefit. It is a survival tool, not a prediction tool.