I just realized that many new traders don't really understand what lot size is in trading, and that's a serious problem. Let me explain why it's literally the first thing you should master before putting real money in.

In forex, unlike stocks where you buy individual units, everything works with lots. It's the basic unit to measure the size of your position. Imagine you have to write the order like this: 'I want to invest three hundred twenty-seven thousand eight hundred twelve euros in EUR/USD.' That would be chaos. That's why lot size exists in trading as a standardized measure. One lot equals 100,000 units of the base currency. Two lots are 200,000. Simple.

Now, not everyone has 100,000 euros available for a trade. That's why there are mini lots (10,000 units) and micro lots (1,000 units). In practice, they are represented like this: you write 1 for a full lot, 0.1 for a mini lot, and 0.01 for a micro lot. Most beginners start with micro lots precisely because of this. It's much safer while you're learning.

The obvious question is: how do I invest if I don't have 100,000 euros? This is where leverage comes in. If your broker offers you 1:200 on EUR/USD, each euro you risk behaves as if it were 200 euros. So, to control 1 lot (100,000 euros), you only need 500 euros in your account. But remember, leverage is a double-edged sword.

When you calculate lot size in trading, the math is straightforward. Let's say you want to open a position of 300,000 dollars in USD/CHF. Divide 300,000 by 100,000 and you get 3 lots. Want 20,000 pounds in GBP/JPY? That's 0.2 lots. 7,000 Canadian dollars in CAD/USD? That's 0.07 lots. With practice, you do this mentally.

Now comes the part that really matters: the relationship between lot size in trading and pips. Pips are very small price variations, equivalent to 0.01% or typically the fourth decimal in a pair. If EUR/USD rises from 1.1216 to 1.1218, that's 2 pips. The profit or loss you get depends on how many lots you have open multiplied by how many pips the market moves.

The formula is: Lots × 100,000 × 0.0001 × pips = profit/loss. Example: 3 lots in EUR/USD, the market moves in your favor by 4 pips. So, 3 × 100,000 × 0.0001 × 4 = 120 euros profit. There's a more intuitive method using equivalences: each lot gains or loses 10 euros per pip, each mini lot 1 euro per pip, each micro lot 0.1 euros. So, 3 lots × 4 pips × 10 = 120 euros. Much easier.

There is also the concept of pipettes, which is the fifth decimal (0.001%). It gives greater precision but changes the equivalences. With pipettes, one lot gains or loses 1 euro per pipette, not 10. That is, if your position moves up 34 pipettes, 3 lots × 34 × 1 = 102 euros.

The real skill is choosing the correct lot size for your capital and risk tolerance. This is where many fail. You need to know three things: your available capital, how much you're willing to lose per trade (usually 1-5% of your account), and where you'll place your stop-loss.

Practical example: a 5,000 euro account, you want to risk a maximum of 5% per trade (that's 250 euros). You're trading EUR/USD at 1.1216 and place a stop-loss 30 pips away. The formula is: Risk capital ÷ (stop-loss distance × pip value) = optimal size. So, 250 ÷ (30 × 0.0001) = 250 ÷ 0.003 = approximately 1.25 lots. That's your ideal size for that trade.

What happens if you ignore all this? Margin call. When you use leverage and the market moves against you, your available margin decreases. If it reaches 100%, the broker automatically closes positions without asking. It's brutal. The only defense is to use sensible lot sizes and always set a stop-loss.

It's not complicated, but it does require discipline. Calculate your lot size in trading before each trade, stick to your risk plan, and forget greed. The difference between traders who last years and traders who lose everything is here, in these seemingly boring details.