How to use the position size calculator
- Enter your account balance and pick its currency. Use the balance you trade from, not your total net worth.
- Choose how you size risk. Either a percentage of the balance (the usual choice) or a fixed amount in money.
- Enter your entry price and your stop loss. A stop below the entry makes the trade a long, a stop above it makes a short. The calculator works out the side for you.
- Add a target if you have one, to see the reward and the reward to risk ratio. The target is optional.
- Set the contract multiplier, fees and rounding if they apply. Shares and coins use a multiplier of 1. A futures contract uses its point value.
The answer updates as you type, and the chart shows the trade on a price axis with the money at stake on each side of the entry. The address bar always holds a link to your exact numbers, so you can copy it into a chat, a journal entry or a forum thread.
The position size formula
Position sizing starts from the loss you accept, not from the amount you want to invest. The formula has two steps:
risk amount = account balance × risk percent
position size = risk amount ÷ (stop distance × multiplier + fees per unit)
The stop distance is the gap between your entry and your stop, in price. The multiplier is what one unit gains or loses when the price moves by 1.0. It is 1 for a share or a coin and larger for contracts. Fees per unit is the round-trip commission for one unit, because a stop that costs fees loses more than the price move alone.
Because the stop distance sits in the denominator, a wider stop always means a smaller position for the same risk. That is the point of the formula: the stop goes where the trade is wrong, and the size follows from it.
Worked example
You trade a $10,000 account, risk 1% per trade and want to buy a stock at $150 with a stop at $145 and a target at $165.
If the stop is hit you lose $100, which is 1% of the account. If the target is hit you make $300. Those are the defaults in the calculator above.
How much should you risk per trade?
There is no number that suits everyone, and a calculator cannot choose it for you. Many traders keep risk per trade between 0.5% and 2% of the account, and prop-firm traders often go lower because the firm's daily loss limit is tight. What matters is that the number is fixed in advance and that you can survive a bad streak at that size.
To see how your risk level interacts with your win rate and your average win, run the same inputs through the risk of ruin calculator. Risking 2% instead of 1% looks like a small change until a ten-trade losing streak turns it into a 20% drawdown rather than 10%. The glossary entries on risk per trade and position size cover the idea in more depth.
Position size for stocks, forex, crypto and futures
The formula is the same everywhere. What changes is the unit and the rounding.
- Stocks and ETFs. Whole shares, so set the rounding to 1. The calculator rounds down and shows the risk you actually take after rounding.
- Forex. Positions are measured in lots and stops in pips. Use the forex lot size calculator, which handles pip values and your account currency.
- Crypto. Units can be fractional, so leave the rounding on exact or on the exchange's step. Leverage changes the margin you post, not the risk. The stop distance and the size decide the risk.
- Futures. Enter the contract's point value as the multiplier: $50 for an E-mini S&P 500 contract, $5 for a Micro E-mini S&P 500, $20 for an E-mini Nasdaq-100 and $2 for a Micro E-mini Nasdaq-100. Futures trade in whole contracts, so round to 1.
Common position sizing mistakes
- Sizing from leverage instead of the stop. The margin your broker allows says nothing about how much you should lose. Size from the stop.
- Moving the stop after you have sized the trade. A wider stop with the same size risks more than you planned. See moving the stop.
- Ignoring fees and slippage. Commissions add to the loss per unit, and a stop can fill beyond its price. Read about slippage before you trust a very tight stop.
- Rounding up. Rounding the size up risks more than you chose. This calculator always rounds down.
- Using the wrong multiplier. A contract that moves $50 per point sized as if it moved $1 is fifty times too large.
What the calculator does not know
The result assumes your stop fills at its price. In a fast market, on a gap, or over a weekend, a stop order can fill further away and the loss will exceed the amount shown. The calculator also does not know your margin requirement or your broker's minimum size. Treat the output as the largest size your plan allows, and check it against your platform before you place the order. Nothing here is investment advice.
Frequently asked questions
What is position sizing?
Position sizing is deciding how many units to trade so that a loss at your stop costs a fixed, pre-agreed amount. It is the main way traders control risk, because it separates the size of the bet from the price of the instrument.
How do I calculate position size from a stop loss?
Multiply your balance by your risk percentage to get the money you will risk. Divide that by the distance between your entry and your stop, multiplied by the contract multiplier. With $10,000, 1% risk, an entry at 150 and a stop at 145, the size is $100 ÷ $5 = 20 units.
What percentage of my account should I risk per trade?
There is no single right answer. Many traders risk between 0.5% and 2% per trade. The right figure depends on your win rate, your reward to risk, how many trades you take and how deep a drawdown you can tolerate. The risk of ruin calculator shows what each level does over a run of trades.
Does leverage change my position size?
No. Leverage changes how much margin your broker holds, not how much you lose when your stop is hit. Your loss is the position size times the stop distance. A highly leveraged account lets you open a size that risks far too much, so size from the stop, not from the leverage available.
How do I calculate position size for forex?
Forex stops are measured in pips and positions in lots. You need the pip value of the pair in your account currency, then divide your risk amount by the stop in pips times that pip value. The forex lot size calculator does this and fills in the exchange rate for you.
Why does the calculator round the size down?
Rounding up would put more money at risk than you chose. Rounding down keeps the loss at or below your limit. The calculator also shows the risk you actually take after rounding, which can be a little lower than the budget.
Can I use it for short trades?
Yes. Put the stop above your entry and the calculator treats the trade as a short. The size and the risk use the same formula. The target for a short must sit below the entry.
How do fees change the position size?
Fees raise the loss per unit, so the size gets smaller. If the round-trip fee is $0.50 per share on a $5 stop, each share can lose $5.50, and $100 of risk buys about 18 shares instead of 20. Enter your fee per unit in the calculator to include it.