You should use a calculator on every trade. But knowing how to calculate position size manually is a genuine skill — it forces you to understand the math rather than just copy numbers, and it serves as a backup when tools aren’t available.
Here is the complete manual method.
The 3-Step Manual Formula
Step 1: Dollar Risk = Account Balance × (Risk % ÷ 100)
Step 2: SL Pips = |Entry Price − Stop Loss| ÷ Pip Size
Step 3: Lot Size = Dollar Risk ÷ (SL Pips × Pip Value per Lot)These three steps work for every instrument. The only variable that changes between instruments is the pip value in Step 3.
Pip Values You Need to Memorize
For manual calculation, you need these five numbers in memory:
| Instrument | Pip Value (Standard Lot) | Notes |
|---|---|---|
| EUR/USD | $10.00 | Clean — divide by 10 for mini lots |
| GBP/USD | $10.00 | Same as EUR/USD |
| XAUUSD (Gold) | $10.00 | Same as major pairs — pip = $0.01 move |
| USD/JPY | ~$7.00 | Approximate — varies with rate |
| NAS100 | $1.00/point | Per standard lot per index point |
For rough mental math, assume $10 per pip for everything except JPY ($7) and indices ($1). This gets you within 10–15% of the correct lot size — acceptable for approximation, not for actual trade entry on large accounts.
Worked Example 1: EUR/USD
Setup: $10,000 account, 1% risk, entry 1.08500, stop 1.08200 (30-pip stop)
Step 1: Dollar Risk = $10,000 × 1% = $100
Step 2: SL Pips = (1.08500 − 1.08200) ÷ 0.0001 = 30 pips
Step 3: Lot Size = $100 ÷ (30 × $10) = $100 ÷ $300 = 0.33 lotsRound down to 0.30 lots for safety. Never round up when doing mental math.
Worked Example 2: Gold (XAUUSD)
Setup: $25,000 account, 0.5% risk, entry $2,310, stop $2,210 (100-pip stop)
Step 1: Dollar Risk = $25,000 × 0.5% = $125
Step 2: SL Pips = ($2,310 − $2,210) ÷ $0.01 = 100 pips
Step 3: Lot Size = $125 ÷ (100 × $10) = $125 ÷ $1,000 = 0.13 lotsGold’s pip size is $0.01 (one cent per troy ounce). A $100 price move on gold equals 10,000 pips. Many traders incorrectly count $100 gold move as “100 pips” when it’s actually 10,000 pips — which is why the TRADE90 calculator handles this automatically.
Simplified: use $100 price distance as the “pip equivalent” with $10 pip value. $100 move = $100 risk at 0.10 lots. Check: 0.10 lots × $10/pip × 10,000 pips = $10,000 — no, the pip math doesn’t simplify cleanly. Use the TRADE90 calculator for gold rather than mental math.
Worked Example 3: USD/JPY
Setup: $10,000 account, 1% risk ($100), entry 149.00, stop 148.50 (50-pip stop)
Step 1: Dollar Risk = $100
Step 2: SL Pips = (149.00 − 148.50) ÷ 0.01 = 50 pips
Step 3: Lot Size = $100 ÷ (50 × $7) = $100 ÷ $350 ≈ 0.29 lotsUse $7 as the approximate JPY pip value. The actual value is ≈ $10,000 ÷ current rate. At 149.00 USD/JPY: $10,000 ÷ 149 = $67.11 per pip per lot → $6.71 per pip per 0.10 lot. Use $7 as your mental shortcut.
Manual Sizing Quick Reference Table
Memorize or print this table for the most common setups:
$10,000 Account, 1% Risk ($100)
| Stop (pips) | EUR/USD | XAUUSD | USD/JPY (approx) | NAS100 (points) |
|---|---|---|---|---|
| 20 | 0.50 lots | 0.50 lots | 0.71 lots | 5.00 lots |
| 30 | 0.33 lots | 0.33 lots | 0.48 lots | 3.33 lots |
| 50 | 0.20 lots | 0.20 lots | 0.29 lots | 2.00 lots |
| 80 | 0.13 lots | 0.13 lots | 0.18 lots | 1.25 lots |
| 100 | 0.10 lots | 0.10 lots | 0.14 lots | 1.00 lot |
$25,000 Account, 0.5% Risk ($125)
| Stop (pips) | EUR/USD | XAUUSD | NAS100 (points) |
|---|---|---|---|
| 50 | 0.25 lots | 0.25 lots | 2.50 lots |
| 100 | 0.13 lots | 0.13 lots | 1.25 lots |
| 150 | 0.08 lots | 0.08 lots | 0.83 lots |
| 200 | 0.06 lots | 0.06 lots | 0.63 lots |
The Approximation Rule When Rounding
When the calculation gives a decimal (0.33 lots, 0.17 lots), always round down to the nearest available lot increment:
- 0.33 → 0.30 lots (or 0.33 if your broker supports it)
- 0.17 → 0.15 lots (or 0.17 if supported)
- 0.29 → 0.25 lots
Rounding down slightly reduces your dollar risk. Rounding up increases it beyond your plan — never acceptable.
When to Use Manual vs Calculator
| Situation | Method |
|---|---|
| Routine trade on familiar instrument | Calculator (10 sec) |
| No internet/app available | Manual (30 sec) |
| Quick sanity check before entering order | Mental approximation |
| Large account ($50k+) | Calculator only — no mental math |
| Funded account evaluation | Calculator only — no exceptions |
| Unfamiliar instrument or cross pair | Calculator only |
Manual calculation is a backup skill, not a preferred method. Use the TRADE90 position size calculator on every trade when possible — it eliminates calculation errors and handles pip value variations automatically.
Frequently Asked Questions
Can I calculate lot size in my head? Yes, for familiar instruments with round-number accounts and stops. The math simplifies cleanly for EUR/USD at $10/pip. For cross pairs, JPY pairs, and indices, always use a calculator.
What is the easiest position size formula? Dollar Risk ÷ (Stop Pips × Pip Value) = Lot Size. Three numbers in, one number out.
What pip values should I memorize? EUR/USD $10, GBP/USD $10, XAUUSD $10, NAS100 $1, USD/JPY ~$7. Everything else: use the calculator.
Is mental math safe for position sizing? For small accounts on familiar instruments, approximation is acceptable as a quick check. Never use mental math as the primary calculation on large accounts or funded evaluations.
What if I make a mental math error? Your broker order window shows the trade value before you confirm. Always check the dollar amount at risk before clicking OK — this catches most sizing errors regardless of how you calculated.