Position Size Calculator
Decide what you're willing to lose first — then let that set the size.
Risk
Standard model — flat maintenance margin rate.
Assumptions (all editable)
The maintenance margin rate is only used for the liquidation cross-check below the result.
Result
E3 · Modelled Estimate
Stop sits — in front of the estimated liquidation price.
Calculation and assumptions
Educational tool, not investment advice.
A worked example
A $10,000 account risking 1% on one trade, with the stop placed 2% below entry. The size falls out of those decisions rather than being chosen first.
What goes in
- Account equity
- $10,000
- Risk per trade
- 1% — $100
- Entry price
- $60,000
- Stop price
- $58,800 (−2%)
- Leverage
- 10x
- Quantity step
- 0.001
- Costs
- 0.05% taker, 0.02% slippage
What comes out
- Position size
- 0.078 BTC
- Position notional
- $4,680.00
- Required margin
- $468.00
- Risk if stopped
- $99.15 — 0.99% of equity
- Liquidation (est.)
- $54,298.65
- Stop sits in front of liquidation by
- 7.50%
The arithmetic is: $100 of budget divided by what one coin loses if the stop fills. That per-unit loss is not just the $1,200 price move — it also carries the fee to get in, the fee to get out, and an allowance for the stop filling slightly worse than its price. Together they make each coin lose about $1,281, which is why the answer is 0.078 rather than 0.083.
The result is then rounded down to the exchange's quantity step, never up. Rounding up would push the real risk past the budget you just set, which would defeat the point of the tool. That rounding is why the risk shown is $99.15 rather than exactly $100.
Leverage did not decide the size — risk and stop distance did. What leverage decided is the $468 of margin needed to hold it, and where liquidation sits. Notice liquidation is 7.5% below the stop: the stop gets hit first, which is the arrangement you want. If that number ever goes negative, the exchange would close the position before your stop fires.
What each field means
- Account equity
- The account this trade is sized against. It stays on this page — it is not carried to other tools.
- Risk per trade
- How much of the account may be lost if the stop fills, as a percentage or a cash amount. The two stay in sync; whichever you type is the one that counts.
- Entry price and stop price
- The stop is not a hope, it is where the idea is wrong. Its distance from entry is what sizes the trade: a tighter stop buys a bigger position for the same risk, a wider one a smaller.
- Leverage
- Decides the margin required and the liquidation price. It does not change the position size that your risk budget allows.
- Quantity step
- The smallest increment your exchange accepts for this contract. The result is rounded down to a multiple of it.
- Slippage on stop
- How much worse than the stop price you expect the fill. Stops fill into moving markets; a stop that fills exactly at its price is a good day, not the base case.
Common questions
Why is the size smaller than risk divided by stop distance?
Because fees and slippage are part of the loss. Getting in costs a fee, getting stopped out costs another, and the stop rarely fills exactly at its price. Those come out of the same budget as the price move, so the size that fits the budget is smaller than the naive calculation suggests. Turning costs off shows the difference.
Does higher leverage let me take a bigger position?
Not for the same risk. Position size here is set by your risk budget and stop distance — both of which leverage leaves untouched. What higher leverage changes is how much margin you must post, and how close liquidation sits. Raise it far enough and liquidation moves in front of your stop, at which point the tool warns you, because the stop can no longer do its job.
What does it mean when the tool says the trade doesn't fit my risk limit?
That even the smallest order the exchange will accept loses more than your budget if the stop fills. There is no size that fits, so the honest options are a wider budget, a closer stop, or not taking the trade. Moving the stop closer purely to make the size work changes where the idea is wrong, which is a different decision from sizing it.
Why does a position-size tool care about liquidation?
Because a stop behind the liquidation price is not a stop. The exchange closes the position first, you take the full liquidation loss instead of your planned loss, and the risk number this tool gave you would have been fiction. Checking it is the difference between a plan and a guess.
Should I use the maker fee instead?
If your entry rests as a limit order and actually fills as a maker, your real cost is lower and this tool is being slightly conservative — which is the right direction to be wrong in. The stop side almost always pays the taker fee, since it crosses the book to get out.