What is Position Sizing and How Do I Calculate It?

Position sizing is where the rubber meets the road. You can have a great strategy, but if your position size is wrong, you'll either leave money on the table or blow up your account.

The basic formula is simple:

Position Size = (Account Risk) ÷ (Stop Loss Distance)

Let's break it down with an example.

Your account is $10,000. You decide to risk 2% per trade, which is $200. You're looking at a stock trading at $50. You think it's going higher, so you set a stop loss at $48. The distance between entry and stop is $2.

Position Size = $200 ÷ $2 = 100 shares

You buy 100 shares. If the stock hits $48, you sell and lose $200. If it hits $52, you're up $200. The math protects you.

Why does this matter?

Without position sizing, you might buy 500 shares because "it feels like the move will be big." Or you buy 10 shares because you're scared. Both are mistakes. Position sizing removes emotion. The math decides how many shares you get, based on risk.

Here's another example with a wider stop loss.

You're looking at a longer-term trade. Your account is $50,000. You risk 1.5%, which is $750. The stock is at $100. You set a stop loss at $90 (a $10 move).

Position Size = $750 ÷ $10 = 75 shares

You buy 75 shares at $100. If it drops to $90, you lose $750. If it goes to $110, you win $750.

What if you're trading options or futures?

The principle is the same, but the units change. Instead of shares, you're calculating contracts or option contracts. The formula stays the same: divide your dollar risk by the dollar risk per contract.

Let's say you're trading a futures contract. One contract controls 100 units. Each $1 move in the contract equals $100 in your account. You want to risk $500. Your stop loss is 5 points away.

Position Size = $500 ÷ ($5 × $100) = $500 ÷ $500 = 1 contract

You trade 1 contract. If you go 5 points against you, you lose $500.

The bigger picture:

Most beginners reverse this. They decide how many shares they want to buy, then set a stop loss. That's backwards. You set your risk first (1-2% of account), then your stop loss distance (based on technical support/resistance), then calculate position size.

Position Size → Entry → Stop Loss (Professional way) Position Size ← Entry ← Stop Loss (Beginner way, leads to inconsistent risk)

Once you nail position sizing, every trade has the same dollar risk. Your emotions settle down. You stop thinking "I need to buy 500 shares to make $1,000." You think "Based on my setup, I can risk $200, and that gets me 50 shares." The math is clean.

Position sizing is the mechanic that turns a trading plan into a real system.