A lot size calculator works out the right position size for a single trade based on your account balance, risk tolerance, and stop-loss distance. The output is a lot size in standard, mini, or micro lots that keeps your dollar risk per trade at a constant fraction of equity (typically 0.5 to 1 percent). Use this calculator before every manual trade, and configure your Expert Advisor with the same risk-per-trade rule so position sizing scales automatically as your account grows.
Lot Size Calculator
How the Lot size calculator works
Lot size = (Account balance * Risk %) / (Stop loss in pips * Pip value per standard lot). Example: a $5,000 account risking 1 percent ($50) on a 50-pip stop on EURUSD (10 USD per pip per standard lot) gives lot size = 50 / (50 * 10) = 0.10 standard lots. The calculator above accepts your pip value in account currency, which you can compute with the pip value calculator if you trade pairs other than USD-quoted majors.
Frequently asked questions about the lot size calculator
What is the right risk per trade for an EA?
Most professional traders risk 0.5 to 1 percent of account equity per trade. Risking 2 percent or more is aggressive and can lead to large drawdowns during losing streaks. For prop firm challenges with tight daily-loss limits, 0.5 percent is the safer choice.
How do I find the pip value for my pair?
Use the pip value calculator linked below this calculator. For USD-quoted majors (EURUSD, GBPUSD, AUDUSD), one pip per standard lot equals 10 USD. For JPY pairs, the pip value depends on the current USDJPY rate. For gold, broker contract conventions vary.
Why does lot size matter for EAs?
EAs that use fixed lot sizes break down as account equity changes. A 0.10-lot trade is 2 percent risk on a $250 account but only 0.1 percent on a $5,000 account. Risk-percent sizing scales with the account and keeps drawdown predictable.
What is the difference between standard, mini, and micro lots?
A standard lot is 100,000 units of the base currency. A mini lot is 10,000 units (0.10 standard lot). A micro lot is 1,000 units (0.01 standard lot). Smaller lots reduce risk and let you trade smaller accounts without breaking position sizing rules.
How do I configure lot size in an EA?
Most EAs have a Lot Size or Risk Per Trade parameter in the settings dialog. Risk Per Trade is the safer choice because the EA computes lot size automatically from current equity. If your EA only accepts fixed lot sizes, recompute the lot size with this calculator whenever your balance changes materially.