How to Calculate Lot Size (Plain English Walkthrough)

Lot size is the number of standard units you're trading on a given position. One standard lot in forex is 100,000 units of the base currency. A mini lot is 10,000 units (0.1 standard lot). A micro lot is 1,000 units (0.01 standard lot). Most retail traders use mini and micro lots — only well-capitalized accounts trade in standard lots regularly. Picking the right lot size is the most important thing you'll do on any trade because it determines your dollar risk. Here's the principle that separates pros from beginners. Lot size is OUTPUT, not input. You don't decide "I'll trade 0.5 lots today." You decide three things in this exact order: how much of my account am I willing to lose on this trade (risk percent → dollars), where does my stop loss go (chart structure → stop distance in pips), and what is my pip value (depends on the pair). Then the lot size falls out of the math automatically. The formula handles it. The formula: lot size = (account risk in dollars) / (stop in pips × pip value per pip per standard lot). Worked example. $5,000 account, 1% risk ($50), trading EUR/USD with a 30 pip stop. Pip value on EUR/USD = $10 per pip per standard lot. Lot size = $50 / (30 × $10) = $50 / $300 = 0.167 standard lots. Round DOWN to 0.16 lots (never up). Enter the trade at 0.16 lots. If the stop hits, you lose exactly $48. If price hits a 60 pip target, you make $96. Second example. $1,000 account, 1% risk ($10), trading XAUUSD (gold) with a 50 pip stop where one pip = $1 per micro lot ($10 per standard lot). Lot size = $10 / (50 × $10) = $10 / $500 = 0.02 standard lots. Enter the trade at 0.02 lots. Notice how on a smaller account, lot size naturally gets smaller — that's the math protecting you from oversizing. Common mistakes. Using the same lot size on every trade regardless of stop distance (this gives wildly different dollar risks). Rounding up instead of down (this puts you over your risk limit on every trade — small leak, big damage over hundreds of trades). Skipping the calculation when the trade "feels strong" (conviction has nothing to do with risk math; the formula doesn't care). Using leverage as the input instead of risk percent (leverage is a maximum, not a target). Run the calculation on every single trade. Yes, every one. The 30 seconds it takes is what keeps you in the game.