Position Sizing — The Lot-Size Formula Pros Use

The last chapter said "never lose more than 1%." But the question is — how do you know how many lots to open so that you lose exactly 1%?

Beginners size by "feel" — "this one looks solid, go big" · "not sure about this one, go small."

Wrong — and dangerously so — because the trade you feel most confident about is the most dangerous one (high confidence = low caution).

Pros calculate position size with one formula, every trade, no exceptions:

> Position Size = (money you will risk) ÷ (Stop Loss distance × value per point)

Here is a real example, step by step:

Step 1 — find the money you will risk. $10,000 account · 1% rule → risk = $100.

Step 2 — measure the Stop Loss distance. You analysed the chart and the correct SL (below the swing low) sits 50 pips from entry.

Step 3 — plug into the formula. $100 ÷ 50 pips = $2 per pip you can tolerate.

Step 4 — convert to lots. EUR/USD: 1.00 lot ≈ $10/pip → you want $2/pip → open 0.20 lot.

Done. No matter how "confident" you feel, the answer is 0.20 lot.

The mistake beginners make most — the SL does not adjust to the lot size; the lot size adjusts to the SL.

Beginners do it backwards: they open the lot size they want first → price moves against them → they slide the SL further out because they "don't want to get stopped."

That is letting position size dictate your fate, instead of letting the plan dictate it.

Pros do the reverse: find the correct SL based on price structure first → then calculate the lot so the risk is exactly 1%.

If a good setup needs a wide SL (say 150 pips) → the lot just gets smaller (0.067 lot) → you still lose $100. If a setup allows a tight SL (say 20 pips) → the lot can be larger (0.5 lot) → still a $100 risk.

The risk stays constant — what changes is the lot.

This is why pros prefer setups where the SL can be tight — not because they "win more often," but because the R:R is better: at a short SL distance, the same target is a larger multiple of the risk.

Tool: TradingView's "Long/Short Position tool" does this for you — drag entry, SL and TP and it shows the R:R plus the size you should open if you enter your account size.

Make this formula a habit — before every trade, ask three things: Where is the SL? · How much do I lose? · How many lots?

If you cannot answer those three, you are not ready to click buy