Position size is the single most important number in any trade, and most traders pick it by feel. They decide how confident they are, type in a lot size, and hope. That is backwards. Your position size should be the output of how much you are willing to lose, not the input.
This guide gives you one formula that works for every market, then walks through it for forex (lots), stocks (shares) and crypto (units). You will also see how the percent-risk method keeps your losses uniform, and which sizing mistakes quietly drain accounts. If you just want the answer for a specific trade, run it through the position size calculator; if you want to understand the number it gives you, read on.
The One Formula You Need
Every position-sizing calculation comes down to a single equation:
Position size = Risk amount ÷ (Stop distance × Value per unit)
Three inputs, and that is the whole thing:
- Risk amount — the cash you are willing to lose if the stop is hit. This is decided before the trade, not after.
- Stop distance — how far your stop-loss sits from your entry, measured in the unit your market uses (pips, points, dollars per share, or price units).
- Value per unit — what one unit of stop distance is worth for the smallest tradable size of that instrument (e.g. the dollar value of one pip per lot, or simply $1 per share).
The denominator — stop distance times value per unit — is your loss per unit of size if the trade goes against you. Divide your risk budget by that, and you get exactly how much size you can carry without exceeding the risk you chose. Nothing about your "conviction" enters the math.
Step One: Decide Your Risk Amount (Percent-Risk Sizing)
Before you can size anything, you need a risk amount. The professional default is fixed-fractional risk, also called the percent-risk method: you risk the same small percentage of your account on every trade.
Most disciplined traders use 1% to 2% per trade. On a $10,000 account, 1% is $100. That is the most you lose if the stop is hit — regardless of the instrument, the stop width, or how good the setup looks.
The point of fixing the percentage rather than the dollar amount is that it scales with your account automatically. As the account grows, your risk per trade grows with it; as it shrinks during a drawdown, your risk shrinks too, which slows the bleeding when you are trading badly.
Here is what that uniform risk looks like across account sizes at common risk percentages:
| Account size | 0.5% risk | 1% risk | 2% risk |
|---|---|---|---|
| $5,000 | $25 | $50 | $100 |
| $10,000 | $50 | $100 | $200 |
| $25,000 | $125 | $250 | $500 |
| $100,000 | $500 | $1,000 | $2,000 |
Pick one row and one column and commit to it. The discipline of a fixed fraction is what makes your results comparable trade to trade — and what keeps one bad loss from being a catastrophic one.
Worked Example: Forex (Sizing in Lots)
Forex sizing trips people up because of lots and pips, so let us make it concrete. This is illustrative, not a live call.
Say you have a $10,000 account and you risk 1% per trade, so your risk amount is $100. You spot a long on EUR/USD with your stop 25 pips below entry.
For EUR/USD, one pip is worth roughly $1 per mini lot (a mini lot is 0.10 standard lots, or 10,000 units). Plug the numbers in:
- Risk amount = $100
- Stop distance = 25 pips
- Value per unit = $1 per pip, per mini lot
Position size = $100 ÷ (25 × $1) = $100 ÷ $25 = 4 mini lots
Four mini lots is 0.40 standard lots. Let us prove it works: at 0.40 lots, one pip is worth about $4 (since a standard lot is roughly $10/pip, and 0.40 × $10 = $4). A 25-pip loss is 25 × $4 = $100 — exactly your 1% risk. The math closes.
Notice what changed and what did not. If your stop had been 50 pips instead of 25, the position would halve to 2 mini lots ($100 ÷ $50), because a wider stop forces a smaller size to keep the loss at $100. The risk stays pinned at 1%; only the size flexes. That is the whole point.
Worked Example: Stocks (Sizing in Shares)
Stocks are the simplest market to size because "value per unit" is just $1 — one dollar of price move equals one dollar per share. So the formula collapses to:
Shares = Risk amount ÷ Stop distance per share
Say you have a $25,000 account and risk 1%, so your risk amount is $250. You buy a stock at $52.00 and place your stop at $49.50.
- Stop distance per share = $52.00 − $49.50 = $2.50
- Risk amount = $250
Shares = $250 ÷ $2.50 = 100 shares
That position is worth 100 × $52.00 = $5,200 of stock. If the stop is hit, you lose 100 × $2.50 = $250 — your 1% — even though the position itself is over a fifth of your account. This is the lesson most beginners miss: a large position is not the same as a risky one. Your risk is set by the stop distance and the share count, not by the dollar value of the position.
If you traded a more volatile name that needed a $5.00 stop instead, the same $250 budget would buy only 50 shares ($250 ÷ $5.00). Wider stop, smaller size, identical risk.
Worked Example: Crypto (Sizing in Units)
Crypto works exactly like the formula's general form: stop distance is measured in the quote currency (usually USD) and value per unit is $1 per coin per dollar of move, so it again simplifies to risk ÷ stop distance.
Say you have a $5,000 account and risk 2%, so your risk amount is $100. You go long Bitcoin at $60,000 with a stop at $57,000.
- Stop distance = $60,000 − $57,000 = $3,000 per BTC
- Risk amount = $100
Position size = $100 ÷ $3,000 ≈ 0.0333 BTC
That position is worth roughly 0.0333 × $60,000 = $2,000 of Bitcoin. Hit the stop and you lose 0.0333 × $3,000 = $100 — your 2%. Because crypto stops are often wide in dollar terms, the unit size comes out small; that is correct, not a mistake. The formula is protecting you from oversizing into volatility.
If you used leverage to open that $2,000 position with less margin, your risk would not change — the stop still caps the loss at $100 — but your liquidation distance and margin would. Sizing and leverage are separate decisions; see our leverage calculator for that side of the trade.
The Three Markets Side by Side
The denominator is the only thing that really differs between markets. Same formula, three flavours:
| Market | Stop distance unit | Value per unit | Formula shape |
|---|---|---|---|
| Forex | Pips | Pip value per lot (e.g. ~$1/pip per mini lot on EUR/USD) | Risk ÷ (pips × pip value) |
| Stocks | Dollars per share | $1 per share | Risk ÷ stop per share |
| Crypto | Quote currency (USD) | $1 per unit | Risk ÷ stop distance |
Once you internalise that every market is the same equation with a different "value per unit," position sizing stops being three separate skills and becomes one.
Common Position-Sizing Mistakes
Most sizing damage comes from a short list of repeatable errors:
- Sizing by conviction. Doubling up because a setup "feels certain" breaks the uniform-risk principle. Your most confident trades are not statistically your most reliable, and one oversized loser can erase a string of disciplined wins.
- Ignoring the stop. A position size means nothing without a defined stop. If you do not know your stop distance, you cannot calculate size — you are guessing, and the formula has no input to work with.
- Risking a fixed dollar amount that is too large. Risking $500 on a $10,000 account is 5% per trade. A normal losing streak of, say, eight trades is a 40% drawdown — deep enough that recovery becomes very hard. Keep the percentage small.
- Forgetting that wider stops demand smaller size. Traders often keep the same lot size and just move the stop further out "to give it room." That secretly increases the dollars at risk. Widen the stop, shrink the size.
- Confusing position size with leverage. Leverage changes the margin you post, not the risk your stop defines. Sizing first, leverage second.
- Round-number sizing. Trading "1 lot" or "100 shares" because it is tidy, rather than because the math says so, means your risk is random from trade to trade.
If you want to compare a trade's risk against its potential reward before you commit size, pair this with the risk-reward ratio calculator — a trade that passes the R:R filter is the only kind worth sizing in the first place.
Putting It Into Practice
The workflow on every trade is the same four steps:
- Fix your risk amount as a small percentage of your current account balance (1–2% for most traders).
- Find your stop distance from your actual entry and stop-loss levels — never invent one to fit a size you already want.
- Identify the value per unit for your instrument (pip value per lot, $1 per share, $1 per crypto unit).
- Divide to get your size, then round down to the nearest tradable increment so you never exceed your risk.
Do this every time and your losses become uniform and small by design, which is the entire foundation of staying in the game long enough to let an edge play out.
The fastest way to know whether your sizing is actually disciplined is to measure it. Logging every trade in a trading journal lets you check, after the fact, whether your real losses cluster near your intended risk or drift well above it. Over 50–100 trades, that one column — risk taken versus risk planned — tells you more about your survival odds than any win-rate stat. When you want the exact number for a live trade, the position size calculator does the arithmetic in seconds.
FAQ
What percentage of my account should I risk per trade?
Most disciplined traders risk 1% to 2% of their account per trade, and many newer traders start at 0.5% while they are still learning. The exact figure matters less than keeping it small and fixed: risking a uniform percentage means a normal losing streak is a survivable drawdown rather than an account-ending one. As your account grows or shrinks, the dollar amount adjusts automatically because the percentage stays the same.
How do I calculate position size if I don't have a stop-loss?
You cannot — and that is the point. The position-sizing formula requires a stop distance as an input, because your risk is defined by how far price can move against you before you are out. If you are trading without a stop, you have no defined loss, which means no calculable size and effectively unlimited risk. Set the stop first based on the chart (a level that invalidates your idea), then size to it.
Does position size change with leverage?
No. Leverage determines how much margin you post to open a position; it does not change the risk your stop defines. You can open the same position size at different leverage levels and lose exactly the same amount if the stop is hit — the only thing that changes is the margin tied up and how close your liquidation price sits. Size your trade from your stop and risk first, then decide leverage separately.
Why is my calculated position size sometimes a fraction?
That is normal and correct. Wide stops and small risk budgets produce small sizes — for example, 0.0333 BTC or 0.40 lots. Always round down to the nearest size your broker allows so you stay within your intended risk rather than slightly over it. A fractional answer is the formula doing its job, not an error.
About the author. Artem Gasparyan is the founder of GASPNTRADER, a free trading journal built to help traders size positions consistently and turn their results into a measured edge. The methods above reflect standard risk-management practice and are educational, not financial advice.
