Position Sizing — The Formula That Keeps You In The Game

Position sizing is the answer to a single question: how many coins (or how much USD) should I put into this specific trade? It is the most important calculation in trading and the one most beginners get backwards.

The right order of operations

The mistake every beginner makes is this:

1. Decide how much capital to put into the trade ("I'll use 10% of my account")
2. Set the stop loss somewhere

This is backwards. The correct order is:

1. Decide how much of your account you are willing to lose on this trade (the "risk per trade" — usually 0.5–2%).
2. Set the stop loss at the level dictated by chart structure (the "stop distance").
3. Calculate the position size that makes those two numbers consistent.

In equation form:

Position size (USD) = (Account size × Risk%) / Stop distance%

Or expressed in coins:

Position size (coins) = (Account size × Risk%) / (Entry − Stop)

The output is what it is. You do not get to choose the position size — the math does. Your only inputs are the percentage of account you accept losing and the structural stop level.

Worked example

You have a $10,000 account. You decide your max risk per trade is 1%, so $100. You long BTC at $42,000 with stop at $40,700 (stop distance = $1,300, or 3.1% from entry).

Position size = $100 / $1,300 × $42,000 = $3,230 worth of BTC
             = 0.0769 BTC

If the stop hits, your loss is $1,300 × 0.0769 = $100 (1% of the account). Exactly what you decided.

Now run the same trade with a stop at $39,000 (deeper, structural):

Stop distance = $3,000
Position size = $100 / $3,000 × $42,000 = $1,400
             = 0.0333 BTC

The same risk amount ($100) now corresponds to a smaller position because the stop is further away. Your downside is the same. Your upside is smaller — but that is correct: a wider stop means more uncertainty, so you take less of it.

The 1% rule

The most widely-used risk-per-trade is 1% of account equity. Some traders go to 2% for high-conviction setups; aggressive traders go to 0.5%. Almost nobody profitable goes above 2%.

Why 1% (and not, say, 5%)? The math of survival.

Losing 14 trades in a row sounds impossible — until it happens. Every trader has streaks. A 14-trade losing streak is statistically routine over a year of active trading with a 40-50% win rate.

At 1% per trade, that streak costs you 13% of your account — survivable. At 5% per trade, it costs you 51% — and now you need a 104% gain just to recover.

This is the "ergodicity" of risk: average outcomes do not equal individual outcomes when single losses can compound. Sizing exists to keep you in the game until the law of large numbers can deliver your edge.

Leverage

In crypto, every retail trader has access to leverage. Leverage does not change the math above — risk per trade is still risk per trade. It only changes the capital efficiency.

A $3,230 BTC long position can be expressed as:

• $3,230 spot purchase (no leverage)
• $3,230 × 5× leverage = $646 margin posted
• $3,230 × 10× leverage = $323 margin posted

In all three cases, the position size and risk are identical. The only difference is how much account capital is locked up as collateral.

Account percentage vs notional size

Many beginners confuse three different numbers:

• Account risk: how much you lose if stopped out (1% of $10,000 = $100).
• Position notional: the total value of the position ($3,230 in the example).
• Margin posted: capital locked up as collateral ($646 at 5× leverage).

These are three separate numbers and they have different jobs. Position sizing is about the first two. Margin is a side effect.

When the Position Size Calculator asks for "Risk per trade," it wants the first number, not any of the others.

Adjustments

The 1% rule is the floor of discipline. Sophisticated traders adjust within a range:

• High-conviction A+ setup, all confluences aligned: maybe 2%.
• B-grade setup, only most of the criteria checked: 1%.
• C-grade ("this looks ok"): 0.5% or skip.

The key is that the upper bound of your range — even on the best possible setup — is fixed. No "this one is a sure thing, I'll go to 10%." The streaks will find you.

You can also reduce sizing after losses:

• After a 5% drawdown from a recent peak: cut sizing to 0.5%.
• After a 10% drawdown: cut to 0.25% or stop trading until you reset.

This "anti-martingale" approach prevents the death spiral where you size up to "win back" losses and accelerate further into the drawdown.

Common mistakes

• Sizing by gut feel. "I really like this trade, I'll go 5%." Conviction is not statistical — it is psychological. Conviction over-weights recent wins.
• Inverting the relationship. Tightening the stop after you sized the position, so the "1% risk" becomes 0.3% risk with a stop that gets hit by noise.
• Sizing in coins instead of USD. "I always trade 0.1 BTC." That is $4,200 today and $700 in a bad cycle. Always size in USD risk.
• Not adjusting for fees. If round-trip fees + funding are 0.2% on a 3% stop, your real risk is 1.067% on a "1%" trade. The error compounds on small-cap alts with wider spreads.
• Forgetting correlation. Two longs on BTC and ETH at 1% each are not 2% total risk — they are closer to 1.8% because BTC/ETH move together.

In CSAPP

CSAPP signals publish entry, stop, and targets — but they do not publish position size, because that is account-specific. The Position Size Calculator in our tools section takes the signal's entry and stop and your account size, and produces the exact size to use.

Related

• Stop Loss
• Risk/Reward
• Risk Management
• Entry