Position Size Calculator
Calculate how much to buy based on your account size, risk tolerance, entry and stop-loss.
Calculator
For educational and informational purposes only — not financial, investment or tax advice. Results are estimates based on the figures you enter.
Conceptual diagram
What the Position Size Calculator does
The Position Size Calculator answers one of the most important questions in active trading: how large a position can you take given your account size, your willingness to lose a fixed percentage on this trade, and the distance between your entry and stop-loss?
Without this discipline, most traders do the opposite — they choose a position size that “feels right” and then find a stop that fits. This reversal of logic is one of the most common causes of account blowup. The correct sequence is to decide how many dollars you are willing to lose on this specific trade (typically 1–2% of your account), then let the math tell you the correct position size. The calculator enforces that sequence automatically.
The formula
Risk per unit = Entry price − Stop-loss price
Position size (units) = Risk amount ÷ Risk per unit
Position value ($) = Position size × Entry price
Worked example: a Bitcoin long with 1% risk
Illustrative — not a trade recommendation
Account: $20,000. Risk per trade: 1% ($200). Entry: $65,000. Stop-loss: $62,000. Risk per unit: $3,000.
- Position size: $200 ÷ $3,000 = 0.0667 BTC
- Position value: 0.0667 × $65,000 = $4,335
- Account exposure: 21.7%
If the stop fires and the loss is exactly $200, the account is intact at $19,800 — a 1% loss and the trader can continue. The position value (21.7% of account) is meaningful exposure but not dangerously concentrated.
Stop-loss distance determines position size
The most counterintuitive lesson: a wider stop does not mean more protection — it means a smaller position, because the wider gap between entry and stop-loss requires fewer units to keep the risk amount the same.
The risk amount ($200) is identical in all four rows. The position size changes — not the risk. A trader with a stop at $60,000 is not safer than one at $64,000; they are just holding a much smaller position in the same direction.
How risk % changes the outcome
| Account | Risk % | Risk $ | Entry | Stop | Position size | Position value |
|---|---|---|---|---|---|---|
| $20,000 | 0.5% | $100 | $65,000 | $62,000 | 0.033 BTC | $2,167 |
| $20,000 | 1.0% | $200 | $65,000 | $62,000 | 0.067 BTC | $4,335 |
| $20,000 | 2.0% | $400 | $65,000 | $62,000 | 0.133 BTC | $8,670 |
| $20,000 | 5.0% | $1,000 | $65,000 | $62,000 | 0.333 BTC | $21,667 |
At 5% risk, the position value exceeds the account size — implying margin. A stop-loss event loses $1,000 (5% of account). More critically, if the asset falls to zero (not impossible in crypto), the loss is the entire position value — and any leverage multiplies that further. The 1–2% rule exists precisely to survive scenarios like this.
Scenario: ETH short with a tight stop
Short trade example — illustrative
Account: $15,000. Risk: 1.5% ($225). Entry (short): $3,500. Stop-loss (above): $3,570. Risk per unit: $70.
- Position size: $225 ÷ $70 = 3.21 ETH
- Position value: 3.21 × $3,500 = $11,243
- Account exposure: 74.9% — a large portion in one trade
A tight stop ($70 distance) allows a large position for the same risk dollar. This is why tight stops are common — they allow more upside/downside exposure with the same loss ceiling. But tighter stops are also more easily triggered by normal market volatility. There is always a trade-off between risk control and the probability of staying in the trade long enough for the setup to play out.
The 1% rule: why it matters over time
Professional traders typically cap risk per trade at 1–2% of account value. The compounding math behind this discipline shows why it matters so much:
| Risk per trade | After 10 losses in a row | Drawdown | Gain needed to recover |
|---|---|---|---|
| 1% | $18,083 (of $20K) | −9.6% | +10.6% |
| 2% | $16,343 | −18.3% | +22.4% |
| 5% | $11,979 | −40.1% | +67.0% |
| 10% | $6,974 | −65.1% | +186.7% |
No trader wins every trade. The size discipline is what allows a sound system to survive the inevitable losing streaks long enough to be profitable in aggregate. At 10% risk, ten consecutive losses — a plausible scenario for any system — leaves the account down 65%, requiring nearly a tripling just to recover.
How to use the calculator
- Enter your account size in USD.
- Set your risk percentage — 1% is a good starting point. Experienced traders rarely exceed 2% per trade.
- Enter the entry price — the price at which you plan to buy (for a long) or sell (for a short).
- Enter the stop-loss price — place this at a technically meaningful level (below a support zone for longs, above resistance for shorts), not at an arbitrary round number where many other traders have their stops.
- Read the position size (units to trade) and position value (total exposure). If the value looks too large relative to your account, widen the stop or lower the risk %.
- Verify the position value fits within your exchange’s available balance or margin limit.
Common mistakes to avoid
- Choosing position size first, stop second. The correct sequence is: decide the stop-loss level → set the risk amount → calculate position size. Never fit a stop around a position size you have already committed to.
- Setting stops at round numbers. Round price levels are where most stops cluster — making them targets for algorithmic traders and market makers. Place stops at technically significant levels, not at $60,000 or $3,000 just because they are round.
- Ignoring fees in the risk calculation. A $200 risk budget at 0.25% fees on a $4,335 position means roughly $21.68 in fees — meaning only $178 of the $200 budget is actual price movement risk. For very small accounts or very tight risk limits, this difference matters.
- Using too high a risk percentage. 5% or higher per trade turns a typical drawdown into a severe account event. Keep risk at 1–2% until your system is well-tested and proven over at least 100 trades.
Limits to keep in mind
- The calculator works for unleveraged (spot) and simple leveraged trades. For futures with funding rates or options with premiums, the actual risk is more complex than this model shows.
- Slippage can cause the actual exit price to differ from the planned stop price, especially on large orders or in illiquid markets.
- Gapping — where price jumps past the stop without trading at that level — can cause losses to exceed the planned risk amount in fast-moving or low-liquidity markets.
Common questions
What percentage of my account should I risk per trade? A common starting point is 1%. Professional traders often use 0.5%–2%. Anything above 3% dramatically increases the probability of a catastrophic drawdown from a normal sequence of losing trades.
How is this different from the profit/loss calculator? The position size calculator is for planning before you enter. The profit/loss calculator is for auditing results after you close the trade. Use them in sequence: size before, audit after.
What if the calculated position size is below the exchange’s minimum order? The trade does not meet your risk parameters at the current stop distance and account size. Options: widen the stop (which shrinks the position to an even smaller size — not helpful), increase the account, or skip the trade.
Does this work for short selling? Yes. For a short, the stop-loss is above the entry price. Enter the entry price and stop-loss price as normal — the calculator works in either direction. Risk per unit is always the absolute difference between entry and stop.
Related reading
- Glossary: Stop-loss, Volatility and Leverage
- Related tools: Profit / Loss Calculator and ROI Calculator
- Guides: Understanding Crypto Risk and Volatility
For education only — not financial, investment or tax advice. Position sizing manages risk; it does not guarantee any outcome.