risk-management
What is position size? How to size a trade by risk
Understand position size in money terms: start with the amount you are willing to lose, stop distance and the instrument's contract data before choosing lots.
Position size is the size of the position you open. On MT5, traders usually see this as lots, but the lot number is only the final output. The more useful question is: if the stop loss is hit, how much money are you actually risking?
A common mistake is using the same lot size on every trade, for example 0.10 lots whether the stop is 50 points away or 500 points away. That makes the monetary risk vary sharply even though the displayed volume looks identical.
A simpler way to think about sizing
Work in this order:
- Balance or equity used as the risk base.
- Maximum cash loss you are willing to accept if the idea is wrong.
- Distance from entry to stop loss.
- Contract specification for the exact symbol at your broker.
- Only then calculate the position size.
If the risk budget is 20 USD, the position size should change with the stop distance. A wider stop generally requires a smaller volume; a tighter stop may allow a larger volume, while still respecting tick value, contract size and the broker’s volume rules.
The core relationship
At a conceptual level:
Position size = Risk budget / Loss per unit if the stop is hit
On MT5, the “loss per unit” can depend on tick size, tick value, contract specification, account currency and sometimes a currency conversion. That is why one generic lot-size formula from the internet should not be assumed to work for every broker and every symbol.
Practical example
Suppose the account is 2,000 USD and you choose a 1% risk budget for one trade.
- Risk budget = 20 USD.
- Entry and stop loss are defined by the setup first.
- The sizing tool uses the symbol data to find a volume where a stop-out at the planned stop would produce a theoretical loss close to 20 USD, subject to the broker’s lot step and limits.
The important point is that 1% is not a universal rule. It is only an example. A suitable risk level depends on capital, strategy, expected losing streaks and the trader’s ability to tolerate drawdown.
Why can the same 0.10 lot carry very different risk?
Because risk is not determined by lot size alone. It also depends on:
- stop distance;
- tick value / contract size;
- instrument;
- account setup;
- account currency;
- current price in some calculation models;
- conversion rate when currencies differ.
0.10 lot on EURUSD should not automatically be treated as equivalent to 0.10 lot on XAUUSD or an index CFD.
Three common mistakes
1. Choosing the lot first and the stop second
If the volume is already too large, the trader may be forced to place an unrealistically tight stop simply to reduce the cash loss. A more disciplined order is: setup → invalidation/stop → risk budget → position size.
2. Increasing size to recover losses
A losing streak does not automatically make the next trade more likely to win. Raising volume only because you want to recover money faster can accelerate drawdown far beyond the original plan.
3. Looking only at percentage, not cash
“Risk 1%” sounds small, but on a larger account it can still be an amount you are uncomfortable losing. Look at both the percentage and the actual money.
Position size vs leverage
Leverage affects how much margin is required to control a position; position size determines how much exposure you open. High leverage does not force you to open a large position. Actual trade risk still comes back to volume, stop distance and price movement.
A 30-second pre-trade checklist
- Where is the entry?
- Where is the setup invalidated?
- How much money can I accept losing if the stop is hit?
- Does the calculated volume respect the broker’s minimum, maximum and step size?
- If the minimum volume still risks too much, skip the trade or change the plan rather than forcing the calculation.
Use the Yoshi tool
The Position Size Calculator lets you enter the risk budget, entry/stop and required instrument information. It is designed to show when important data is missing instead of silently inventing a tick value or currency conversion.
Open the Position Size Calculator
The calculator supports risk planning only. It does not guarantee a profitable trade and does not replace checking the contract specification at your broker.