Crypto position size calculator

Enter how much you are willing to lose on a trade and where the stop goes, and this works out how many coins to buy or short. It counts fees and funding, checks the leverage the position needs, and tells you when costs take too much of the risk. It runs in your browser, and nothing is stored or sent.

How the size is worked out

The stop comes first and the size follows from it. The sum has three steps:

1. Cash at stake is the account times the planned loss. On 10,000 at 1% that is 100.
2. Risk per unit is the distance from entry to stop plus the cost per unit. A long at 50 with the stop at 48 and 0.3 of costs risks 2.3 per unit.
3. Units are the cash at stake divided by the risk per unit, rounded down. 100 / 2.3 is 43.47, so 43 units, worth 2,150.

Rounding down keeps the planned loss at or under the limit you set: 43 x 2.3 is 98.9. Those are the numbers the calculator starts on, so you can check it before typing your own.

Leverage is the last thing to set. 2,150 on a 10,000 account is 0.215x, so this trade needs no borrowed exposure. A tight stop is what pushes leverage up: the same 100 at stake with a stop 0.25% from entry calls for a 40,000 position, four times the account.

Working out the cost per unit

Costs belong in the risk because a stopped-out trade pays them too. For a long at 50 held two days on a perpetual, with a 0.06% taker fee and funding of 0.01% every 8 hours:

• Fees on both fills: 50 x 0.06% x 2 = 0.06.
• Funding over six payments: 50 x 0.01% x 6 = 0.03.
• Spread and slippage: whatever your recent fills on that coin show, say 0.21.

That is 0.30 per unit. Funding can be paid or received depending on its sign and your side; count it only when you pay it. Leave the field at 0 to see the size before costs.

What the checks mean

• Position value / account is compared with your leverage ceiling, 3x by default. Over it, the calculator shows the largest size the ceiling allows and the smaller planned loss that goes with it.
• Costs fail when they are more than one fifth of the planned loss, which happens when the stop is less than four times the cost per unit away. The stop is too tight for what the trade costs.
• The room test runs when you add a target. It sets the reward after costs against the risk after costs, and says what share of trades like it would have to reach the target to break even.

What it leaves to you

The sum is for one position on a linear contract, such as a USDT-margined perpetual or spot. A coin-margined (inverse) contract or a contract multiplier needs converting first. It cannot tell you the stop is in the right place, and a gap through the stop can make the real loss bigger than the planned one. Positions in coins that move together add up, so cap the group as well as the trade. Then check the liquidation price on the order ticket, or with the liquidation price calculator, and make sure it sits well beyond the stop.