CYCLEPEDIAThe trading encyclopedia
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Position Size

The amount of asset you buy or sell. Too large a size turns a good setup into an emotional nightmare.

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Who it's for — For those who think trading is guessing the direction. Wrong: trading is guessing the size. A great idea with the wrong size leads to failure.

The Position Size (or simply Size) is the amount of the asset you are buying or selling in a single trade. If you buy 2 Bitcoin, your size is 2 BTC. If you buy 100 Tesla shares, your size is 100.

Choosing the correct size is the most important decision a trader makes before clicking Buy or Sell. The larger the size, the greater the potential profit, but incalculably greater is the psychological pressure and the risk of ruin.

In simple terms — If you bet $10 on a coin flip, you don't care about the outcome and sleep soundly. If you bet your entire house, you will start sweating, screaming at the coin, and probably try to stop it while it's spinning. In trading, if your Size is too big, your emotions (Fear and Greed) will take control, leading you to make irrational choices even before the market hits your stop loss.

L'impatto della Size sull'emotività Size 1% 😎 Controllo totale Size 5% 🤨 Massima attenzione Size 50% 😱 Panico (Tilt) Soglia della logica
The impact of Size on emotions and portfolio. Hover to explore.

The "Sleep-o-meter"

There is an infallible test to know if your Size is too big: the sleep test. If you go to bed thinking about the open position, or if you wake up at night to check your phone to see what the price has done, your size is too big. Period. You must reduce it until the outcome of the trade leaves you in absolute emotional indifference.

How it's calculated (Sizing)

Beginners choose their size randomly ("I'll buy $1,000 worth of stuff"). Professionals calculate the size starting from the Risk:

  1. They decide how much money they are willing to lose if the Stop Loss triggers (e.g., $50).
  2. They measure the distance between the entry price and the Stop Loss.
  3. They adjust the Size mathematically so that, in case of a stop, the loss is exactly $50.

Summary Sheet

  • What it is: The physical or monetary quantity invested in a single trade.
  • Law of Trading: Beyond a certain size, your logic shuts down and your emotions drive.
  • Common mistake: Increasing size after a series of winning trades feeling "invincible" (Euphoria).
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