How to Size a Crypto Position Without Guessing

Most traders decide position size the same way they decide how much coffee to drink: however much feels right that day. Then a losing streak wipes out more than it should have, and the post-mortem always finds the same root cause: the position was too big for the actual risk being taken, not for the conviction behind the trade.

Position sizing is not about how confident you are. It is about how much you can afford to lose on this specific trade before it matters, and letting that number, not your feelings, tell you how much to buy.

The formula

There is one calculation that removes the guesswork:

Position size = (Account balance × Risk %) / (Entry price − Stop-loss price)

Three inputs, no opinions:

• Account balance — total capital you are trading with
• Risk % — the share of that capital you are willing to lose on this one trade, typically 0.5–2% for anyone planning to survive more than a few trades
• Entry vs. stop-loss distance — how far price has to move against you before you are proven wrong and exit

A worked example

Account: $10,000. Risk: 1% ($100). Entry: $83,000. Stop-loss: $81,000 (a $2,000 gap).

Position size = $100 / $2,000 = 0.05 BTC.

That is the whole trade. Not "how much BTC can my margin support," not "how much did the last trade make me," just the amount that turns a wrong call into a $100 lesson instead of a portfolio-moving mistake.

Why leverage makes this worse if you skip the step

Leverage does not change the math above; it changes how tempting it is to skip it. A trader who sizes by "how much margin do I have" instead of "how much am I willing to lose" is one bad week away from a liquidation that has nothing to do with being wrong about direction and everything to do with being wrong about size.

Common mistakes that break the formula

The math is simple. What breaks it is skipping the inputs:

• Sizing from margin available, not risk tolerance. Just because your account can support a bigger position at a given leverage does not mean that position matches how much you actually want to risk. Margin is a limit, not a target.
• Not setting a stop-loss before entering. Without a stop-loss price, the formula has no denominator; there is no way to calculate size correctly, which is exactly why so many traders skip the calculation instead of admitting they have not decided where they are wrong yet.
• Averaging into a losing position without resizing. Adding to a loser changes your average entry and your real risk. If you DCA down, recalculate the position size for the new average and the new distance to your stop, do not just add the same amount again.
• Using the same risk % regardless of setup quality. A high-conviction setup with a tight, well-defined stop can justify sizing near the top of your range. A speculative entry with a wide stop should size smaller, even at the same dollar risk, because a wide stop means more can go wrong before you are proven right or wrong.

Position sizing across multiple open positions

The formula above handles one trade in isolation, but most active traders run more than one position at a time. Two adjustments matter here:

1. Cap total portfolio risk, not just per-trade risk. If you risk 1% per trade but run five correlated positions (five different altcoins that all move with BTC, for example), your real exposure on a single market-wide drop is closer to 5%, not 1%. Treat correlated positions as one combined risk budget, not five independent ones.
2. Reserve capital for the setups you have not seen yet. Sizing every open slot at your maximum risk % leaves nothing for the next high-quality setup that shows up mid-week. Many traders cap themselves at 3-4 concurrent full-size positions and treat anything beyond that as reduced size by default.

Neither of these change the core formula, they just mean the formula needs to run per trade, every time, with the current account balance and current open risk, not the balance you had when you opened your first position this week.

Why the source of the number matters

More traders now ask an AI chatbot to do this math for them mid-trade. The problem is not that the formula is hard, it is that a language model gives you a plausible-sounding answer, not a verified one, and plausible is exactly the failure mode you cannot afford when the output decides how much capital is on the line. Two runs of the same inputs through an LLM can quietly disagree with each other. The formula above cannot: the same account balance, risk %, entry and stop will always produce the same position size, because it is arithmetic, not a guess dressed up as one.

Where this fits into the rest of the trade

Position sizing is upstream of everything else, liquidation price, break-even, funding cost. Get the size wrong and none of those other numbers matter, because you are already risking more than you meant to before the trade even starts.

If you want to run the calculation instead of doing the arithmetic by hand, TradingCalc's position size calculator does exactly this: enter account size, risk %, entry and stop, get the exact position size back, deterministically; the same inputs always produce the same output, checked against a public set of verified test cases rather than asked to "seem right." Free, no signup.

The formula above is the whole method. The calculator just saves you from doing it under pressure, mid-trade, when the temptation to round up "just this once" is strongest, and skips the part where you have to trust that the number someone (or something) gave you is actually correct.