What is position sizing? Meaning, formula and examples

Position sizing is deciding how much money to put into a single trade or investment, based on how much you are willing to lose if it goes wrong. Instead of asking “how much could I make?”, you start from your account size and your stop-loss, then work out how many units to buy so that a bad trade costs only a small, planned share of your capital. It is the most practical part of risk management, and it works the same way for stocks, ETFs, crypto and forex.

What is position sizing, in plain words?

Position sizing is the rule that sets the size of each position in your portfolio. The size is not a guess or a round number: it follows from two inputs you decide before you buy, the share of your account you are prepared to risk and the price at which you admit the trade was wrong.

It helps to separate two numbers that beginners often mix up:

• Position value: what the position is worth. Buy 10 shares at €50 and your position value is €500.
• Account risk: what you actually lose if the trade hits your stop loss. With a stop at €45 you lose €5 per share, so €50 in total.

Proper position sizing controls the second number. A €500 position can be a small risk or a large one, depending on where your stop-loss level sits.

Why is position sizing important?

Position sizing is important because it stops one bad trade, or a run of them, from wrecking your account. Even a sound strategy has losing streaks, and with volatile assets such as crypto those streaks can be long.

Here is what ten losses in a row do to a €10,000 trading account, with the risk per trade taken as a fixed percentage of the current balance:

The maths is the point: small losses are easy to recover from, big ones are not. What position sizing cannot do is turn a losing strategy into a winning one. It limits downside risk; your win rate and the size of your winners still decide whether you make money.

How to calculate position size

To calculate position size you need three numbers: your account size, the percentage you will risk per trade, and the distance between your entry price and your stop-loss.

Position size (units) = account risk ÷ trade risk per unit

Account risk = account size × risk percentage. Trade risk per unit = entry price − stop-loss price.

A worked position size calculation

You have €10,000 in a trading account and use a 1% percent risk rule.

Now change only the stop. With a tighter stop at €78 (€2 per unit) you can buy 50 units, a €4,000 position. With a wider stop at €72 (€8 per unit) you buy 12 units, worth €960. The trade size changes a lot, but the potential loss stays at about €100 each time. That is how position sizing works.

Include costs and round down

Costs come out of the same risk budget. If your broker charges €1 to buy and €1 to sell, and the spread costs another €1, your real risk on the example above is €103, not €100. On US shares, add the currency conversion fee. Then round down to whole shares, or to the minimum order step for crypto. A position size calculator does this arithmetic for you, but you should still understand every input. Our guide to trading fees explains the costs to include.

Common position sizing methods

There is no single best position sizing strategy. These are the methods you will see most often, from simplest to most advanced.

Fixed percentage (fixed fractional) position sizing

The fixed percentage method risks the same share of your account equity on every trade, often between 0.5% and 2%. This is fixed fractional position sizing. Because the percentage applies to your current total account, the euro risk shrinks after losses and grows after wins, which slows the damage in a drawdown. It is the usual starting point because it matches risk to your risk tolerance automatically.

Fixed amount and fixed lots

A fixed amount means you risk the same euro sum, say €50, on every trade. It is simple but does not adapt as your account grows or shrinks. Fixed lots means buying the same amount of units every time, for example 10 shares or 0.1 of a coin. It is the easiest rule and the weakest, because your real risk level changes with every price and stop distance.

Volatility based position sizing

Volatility based position sizing uses the market’s recent swings to set the stop, and therefore the size. A common tool is the average true range (ATR): the average daily price range over, for example, 14 days. Put the stop two ATRs below your entry and the formula does the rest. When market volatility rises, the stop widens and the position automatically gets smaller.

Example: a token trades at €2.00 with an ATR of €0.20. A stop two ATRs away is €0.40 below entry, so with €100 of account risk you buy 250 tokens, a €500 position. This suits volatile markets like crypto, where a tight stop gets hit by ordinary noise.

The Kelly criterion

The Kelly criterion is a betting formula that calculates an optimal bet size from your win rate and your average win compared with your average loss. With a 50% win rate and winners twice the size of losers, full Kelly suggests putting 25% of your capital on each trade. That is far more than most traders could stomach, and it relies on statistics about your own strategy that private investors rarely have. If you use it at all, use a small fraction of the result.

Position sizing with crypto and leverage

The same formula applies to crypto, but the inputs behave differently. Prices move around the clock, a stop-loss order can fill well below your price when the market drops fast, and a coin can lose almost all its value. Treat your stop as a plan, not a promise, and never put money into crypto that you cannot afford to lose.

Leverage makes position sizing more important, not less. With leverage, your position value can be many times the money you put up, and the exchange can close your position (liquidation) before your stop is reached. Most retail traders lose money with CFDs and other leveraged products. In the EU, retail CFD leverage is capped, at 2:1 for crypto CFDs, but even 2:1 doubles your losses as well as your gains.

Position sizing mistakes to avoid

These are the most common ways traders break their own position sizing rules:

• Sizing up after a winning run. Confidence is not an edge. Keep the same risk percentage.
• Doubling after losses. Trying to win back a bad trade by risking more is how small losses become large ones.
• Ignoring correlation. Three crypto positions at 1% each behave more like one 3% bet, because they tend to fall together.
• Trading without a stop. Without a stop-loss price you cannot calculate position size, and your real risk is the whole position.
• Forgetting gaps. Shares can open far below Friday’s close after weekend news. Your loss can then be bigger than planned.

Use the right order types to place your stop, and write your risk per trade down before you click buy.

Position sizing for long-term investors

If you invest €100 a month in an ETF through a savings plan, you do not need a stop-loss formula. For you, position sizing means deciding how much of your portfolio goes into each asset class. For example, if you decide crypto should never be more than 5% of a €20,000 portfolio, your cap is €1,000, however exciting the market looks. Regular, fixed amounts, as in dollar-cost averaging, are a form of position sizing too.

The bottom line

Position sizing turns a vague sense of “not too much” into a number: decide your risk per trade, measure the distance to your stop, divide. It will not make a bad strategy profitable, but it keeps you in the game long enough to find out whether yours works.

Related terms

• Risk management
• Stop-loss
• Leverage
• Volatility
• Portfolio