How to calculate position size for crypto futures, from your stop loss

Most traders pick a position size first and then place a stop wherever it fits. That's backwards. If you want every losing trade to cost you roughly the same amount, the size has to come from the stop, not the other way round.

This guide walks through the calculation for crypto perpetual futures, step by step, with fees included. It's the same method the TradeTurtle position sizer uses.

The idea in one sentence

Decide how much of your account you're willing to lose on this trade, measure how far away your stop is, and divide the first by the second.

Everything else, including leverage, margin and fees, is detail around that one division.

Step 1: Decide your risk per trade

Your risk per trade is the most you're willing to lose if the stop is hit, as a percentage of your account. Many traders use somewhere between 0.5% and 2%. The exact number is your call. What matters is that it's decided before the trade and stays the same from trade to trade.

Turn it into dollars:

Risk budget = account balance × risk %

With a $1,000 account and a 1% rule, your risk budget is $10.

Step 2: Measure the distance to your stop

Place your stop where the trade idea is proven wrong, based on the chart, not on how much you'd like to risk. Then measure the distance:

Stop distance = |entry − stop|

Say you're going long BTC at 60,000 with a stop at 59,400. The stop distance is 600 per BTC, or 1% of the entry price.

Step 3: Divide

Position size = risk budget ÷ stop distance

$10 ÷ 600 = 0.0167 BTC. If the price falls to your stop, you lose 600 on each coin, and 0.0167 × 600 = $10.

Exchanges only let you trade in fixed increments (the "size step" or "lot size"). Always round down to the nearest step so you never go over your budget. With a step of 0.001 BTC, that's 0.016 BTC.

Step 4: Don't forget fees

This is where most sizing spreadsheets go wrong. On perpetual futures you pay a fee to open the position and another to close it, and both are charged on the full position value, not on your margin.

With a taker fee of 0.055% on each side, 0.016 BTC costs about:

• Opening: 0.016 × 60,000 × 0.055% = $0.53
• Closing at the stop: 0.016 × 59,400 × 0.055% = $0.52

So a stop-out would really cost 9.60 + 1.05 = $10.65, which is 1.07% of the account. That's over your 1% rule, and it happens on every losing trade.

To keep fees inside the budget, add them to the cost of each coin before dividing:

Cost per coin = stop distance + (entry + stop) × fee rate

Position size = risk budget ÷ cost per coin, rounded down to the size step

Here: 600 + (60,000 + 59,400) × 0.00055 = 665.67 per BTC. Then $10 ÷ 665.67 = 0.01502, which rounds down to 0.015 BTC.

Check: 0.015 × 600 = $9.00 of price risk, plus $0.99 of fees, is $9.99. That's inside the rule.

Funding payments aren't included here because they depend on how long you hold the trade. On longer trades, keep an eye on them too.

Where leverage comes in (it doesn't change your size)

Here's the part that surprises people: leverage doesn't change how much you lose at the stop. The loss depends only on the position size and the stop distance. Leverage only changes how much margin the exchange locks up, and how close your liquidation price is.

Here's the same 0.015 BTC position at different leverage levels:

Leverage	Position value	Margin used	Rough liquidation price	Loss at the stop
5×	$900	$180	48,300	$9.99
10×	$900	$90	54,300	$9.99
50×	$900	$18	59,100	$9.99
100×	$900	$9	59,700	Liquidated first

Look at the last row. At 100× the rough liquidation price (59,700) is above the stop (59,400), so the exchange would close the position before your stop is ever reached. You'd lose your whole margin, plus a liquidation fee on most exchanges, without the stop ever doing its job.

So the rule of thumb is: size from the stop first, then pick a leverage low enough that the liquidation price sits well beyond the stop.

The liquidation prices in the table are rough estimates. They assume isolated margin and a 0.5% maintenance margin. Your exchange's exact formula, margin tiers and fees will move them, so always check the liquidation price the exchange shows before you confirm.

Sanity checks before you place the trade

Before you place the trade, check that:

• The stop is on the right side. For a long it must be below the entry, for a short above it.
• The margin fits. If the margin is more than your balance, the size is too large for your leverage.
• The size didn't round to zero. With a tight budget and a wide stop, the size can fall below the exchange's minimum. That's a sign the trade doesn't fit your rules.
• Liquidation is well beyond the stop. See above.

The whole calculation

For a 1% rule on a $1,000 account, long BTC at 60,000 with a stop at 59,400, 0.055% fees and a 0.001 size step:

Step	Calculation	Result
Risk budget	1,000 × 1%	$10.00
Stop distance	60,000 − 59,400	600
Cost per coin	600 + 119,400 × 0.00055	665.67
Size	10 ÷ 665.67, rounded down	0.015 BTC
Loss at stop	0.015 × 600 + fees	$9.99 (≈ 1.00%)
Margin at 10×	0.015 × 60,000 ÷ 10	$90

Doing it every time

The maths isn't hard, but it's easy to skip when a setup looks good and the price is moving. That's exactly when it matters most. The TradeTurtle position sizer does all of the above as you type: it sizes from your stop and your risk rule, includes fees, rounds to your size step, and warns you when the stop is on the wrong side, the margin is too big or liquidation comes before your stop. Every trade you log is also checked against your rule afterwards.