Sizing
The stop decidesthe size
Pick where you are wrong and how much of the account that is worth. The quantity falls out of those two numbers and the venue’s own step size — never out of a round number that felt right.
The arithmetic, and the part everyone gets wrong
Risk first, quantity second
The input is a fraction of equity — the amount you accept losing if the stop fills. Divide it by the distance from entry to stop and you have a quantity. The order of operations matters: sizing first and checking the loss afterwards produces a position that is the right size for your confidence and the wrong size for your account.
Rounding is where sizing goes wrong
A venue accepts quantities in steps and prices in ticks, so the computed size is almost never placeable as computed. Rounding it up to the nearest step is a position larger than the one the risk check approved — a small overshoot on every trade, compounding quietly. Everything here rounds down, twice: once to the venue’s step, once when the approval is verified against the values actually being sent.
Leverage does not size anything
Leverage changes the margin a venue asks for, not the loss you take when the stop fills. Treating it as a size multiplier is the single most expensive misunderstanding in retail derivatives trading, and nothing here does it: the same stop and the same risk fraction produce the same quantity at 1x and at 10x.
The account ceiling binds before the venue does
A size that passes the risk-per-trade check can still be refused for exposure, for concentration, or because free margin minus your reserve does not cover it. Those are separate limits and they are checked in order, so the refusal names which one bound rather than reporting a smaller number with no explanation.
Questions about sizing
What if I do not want to set a stop?
Then there is no size to compute, and the risk-per-trade limit has nothing to measure. An order with no stop is refused by the policy that requires one — which is a policy you can change, and a decision you should make deliberately rather than by omission.
Does it account for fees?
The fee is part of the realised result and is applied on the fill, and the effective rate the platform uses is the one your fills actually show — not the venue’s published schedule, which on at least one venue we trade is 0 bp while the fills say 14 bp round trip.
Can I size in units instead?
You can place any quantity you like; the gate then tells you what it implies. The calculator exists because the interesting direction is the other one — from an acceptable loss to a quantity, rather than from a quantity to a loss you discover later.
Try it against a real stop
Paper accounts run the same sizing and the same rounding as funded ones.