In a share account, position size is continuous. You can buy any number of shares and tune the risk to whatever figure you settled on. Futures do not work that way. Size arrives in whole contracts, and the money at stake per unit of price movement is fixed by the contract specification rather than chosen by you. That single fact reorders the entire sizing calculation.
From Points to Money
Two numbers define the conversion. The tick is the smallest increment the contract can move. The tick value is what that increment is worth on one contract. Multiply the number of ticks between entry and stop by the tick value and you have the money risked on a single contract, before costs.
Everything else follows from there. The stop distance you were going to use, expressed in points because that is how the chart is marked, becomes a dollar figure only after passing through the multiplier. That multiplier is a property of the contract rather than of the market, so it does not move when volatility does. Only the number of ticks moves.
The Micro and the Full Size Version
Most popular contracts now exist in more than one size, with the smaller version a fixed fraction of the larger. They track the same underlying and their charts are effectively identical, so it is easy to treat them as interchangeable. They are interchangeable in every respect except the one that matters for sizing.
The smaller contract is what makes risk tunable. A stop distance that would risk more than intended on one full sized contract, with no way to buy half of one, becomes adjustable when the unit is a fraction of that size. Traders with modest accounts frequently discover that their real difficulty was never strategy selection but granularity. The smallest position they could take was already larger than their plan allowed, so every trade was oversized before it began.
Stop Distance Sets the Contract Count
The order of the calculation is worth stating plainly, because reversing it is common. Decide the money you are willing to lose on the trade. Measure the stop distance the setup actually requires, which on an opening range is generally the distance to the far edge or to some structure near it. Divide the first by the money value of that distance on one contract. Round down.
Rounding down is not a detail. Rounding up to reach a tidier number turns a fixed risk into a variable one, and it always rounds in the same direction, so the effect accumulates rather than averaging out. A trader who rounds up whenever the answer is awkward is running a slightly larger strategy than the one they believe they are running, permanently.
Where the Arithmetic Goes Wrong
The frequent failure is a constant contract count. A trader settles on a number of contracts and that is what they trade, on a tight range and a wide one alike. Because the stop distance varies with the range and the contract count does not, the money risked varies by whatever factor the range varies by. A single unusually wide session then costs several times what a normal one does, from a strategy that felt consistently sized throughout.
The other failure is moving between products. The same nominal size looks entirely different across contracts because the multipliers differ. Habit carries the contract count across and the risk changes silently, which is precisely the kind of error that produces a loss nobody can explain afterwards, because nothing about the trade looked unusual at the time it was placed.
Costs Are Measured in the Same Unit
Commission and exchange fees are charged per contract, and on the smaller contracts they represent a much larger proportion of a tick. A strategy taking modest targets on micro contracts can find that costs consume a meaningful share of the edge, while the identical strategy on the full sized version barely registers them.
That is not an argument for trading larger than the account supports. It is an argument for including the round turn cost in the arithmetic from the beginning, so that the size you choose and the target you choose are evaluated together rather than one at a time. A target that clears the costs comfortably at one size may not clear them at another, and the point at which it stops clearing them is a property of the contract you selected.