Position Size Calculator
Work out how many shares, units or contracts to buy so that hitting your stop-loss costs a fixed percentage of your account.
This position size calculator turns a risk decision into a share count. You decide how much of the account you are willing to lose if the trade goes wrong, and the distance from entry to stop settles how many shares to buy — or how many contracts, lots or coins on other instruments.
Formula: units = (balance × risk%) ÷ |entry − stop|
Your figures
Percentage of the balance to risk if the stop is hit.
Results
Position size
50
units / shares / contracts
- Amount at risk
- US$100.00
- Risk per unit
- US$2.00
- Position value
- US$2,500.00
- Position as a share of the account
- 25.00%
- Stop distance from entry
- 4.00%
What this means
Buying 50 units at US$50.00 means a stop at US$48.00 costs US$100.00 — 1.00% of the account. The tighter the stop, the larger the position needed to risk the same amount.
- Assumes the stop fills at the stop price. Slippage, gaps and commission increase the realised loss.
Position size: 50
The link reopens this calculator with the same numbers. Nothing you enter is sent to a server.
Continue with these figures
About the Position Size calculation
It handles shares, contracts, crypto or any instrument priced in a single currency. Enter the account balance, the percentage at risk, and the entry and stop prices, and it works as a risk per trade calculator: the share position size that comes back is whatever makes a stop-out cost exactly that percentage.
The core relationship is that position size is inversely proportional to stop distance. Halving the stop distance doubles the position size at the same risk, which is why a position sizing calculator earns its place: the number has to be recalculated for each trade rather than fixed as a standard quantity.
Position Size formula
risk amount = account balance × (risk % ÷ 100)
risk per unit = |entry − stop|
units = risk amount ÷ risk per unit
position value = units × entry- risk amount
- The cash lost if the stop is hit — the risk budget for this trade.
- risk per unit
- How much each share or unit loses between entry and stop.
- position value
- The capital committed, which is usually much larger than the risk amount.
Risk amount and position value are different numbers and are often confused. Risking 1% of a $10,000 account is $100; if the stop is 4% away from entry, the position committed is $2,500 — a quarter of the account, risking a hundredth of it.
That gap is what makes fixed-fractional sizing work. The amount lost on any single trade stays constant as a share of the account, while the capital committed varies with how far the stop sits from the entry.
When the calculated position value exceeds the account balance, the position can only be opened using margin. The calculator flags this rather than silently returning a size you could not take.
Position Size: a worked example
A $10,000 account risking 1% per trade, buying at $50 with a stop at $48.
- Risk amount10,000 × 1% = $100
- Risk per share|50 − 48| = $2.00
- Shares100 ÷ 2 = 50 shares
- Position value50 × 50 = $2,500
- Share of account2,500 ÷ 10,000 = 25%
50 shares. A stop-out costs $100 — 1% of the account — while committing $2,500, or 25% of it.
How to use the Position Size calculator
- Enter your account balance, using current equity rather than the original deposit.
- Set the risk percentage. This is what you lose if the stop is hit, not the amount committed to the position.
- Enter the entry price you intend to trade at.
- Enter the stop-loss price. It can be above or below the entry — the calculator uses the distance.
- Round the resulting unit count down to a whole number where fractional units are not available.
Limitations of the Position Size calculator
Every calculation makes assumptions. These are the ones that matter here.
- Assumes the stop fills at the stop price. Gaps, particularly overnight and over weekends, can produce a larger loss than calculated.
- Excludes commission, stamp duty and spread, all of which add to the cost of a losing trade.
- Does not check whether the position value exceeds what your account can fund, beyond flagging when it exceeds the balance.
- Treats each trade in isolation. Several correlated positions can risk far more in aggregate than each does individually.
Frequently asked questions about Position Size
What is the difference between position size and position value?
Position size is the number of units. Position value is what those units cost — units times entry price. The risk amount is smaller than both: it is only what you lose if the stop is hit.
Why is the position value so much larger than the risk amount?
Because the stop is close to the entry. Committing $2,500 to risk $100 simply means the stop is 4% away. A wider stop would commit less capital to risk the same amount.
Should I use account balance or equity?
Equity — the balance adjusted for open profit and loss — is the more accurate base, since it reflects what the account is actually worth at that moment.
Does this work for forex?
It works if you convert to units of the base currency yourself. The forex position size calculator is easier for currency pairs because it handles pip sizes and the conversion into your account currency.
What if the calculated position is larger than my account?
That means the stop is very tight relative to your risk budget, and the position can only be opened with margin. The calculator flags it. Widening the stop or lowering the risk percentage reduces the size.
Last reviewed . See our methodology and editorial policy.
More trading calculators