The four standard lot fractions
Forex positions are quoted in standardised quantities of the base currency:
1 standard lot = 100,000 units of the base currency. 1 mini lot = 10,000. 1 micro lot = 1,000. 1 nano lot = 100. The notation in trading platforms reflects the lot fraction directly: 1.00 (standard), 0.10 (mini), 0.01 (micro), 0.001 (nano).
Most retail brokers support trading in 0.01-lot increments (micro lots). Some support 0.001-lot increments (nano lots), particularly on smaller accounts. The minimum lot size is set by the broker and may differ between major FX pairs and exotic pairs or commodities. The broker's contract specifications publish the increment for each instrument.
Pip value and {{margin}} scaling with lot size
Pip value scales linearly with lot size. For a USD account on EUR/USD at 1.0850:
1 standard lot (100,000 EUR): $10 per pip, $3,617 margin at 1:30 leverage. 0.10 mini lot (10,000 EUR): $1 per pip, $362 margin. 0.01 micro lot (1,000 EUR): $0.10 per pip, $36 margin. 0.001 nano lot (100 EUR): $0.01 per pip, $3.62 margin.
Both pip value and margin scale by the same factor as the lot fraction. Halving the lot halves both numbers. The Leverage ratio is unchanged — only the position size and the resulting risk and margin commitment change.
Lot size as the position-sizing variable
Position size is calculated from account risk percentage and stop-loss distance, not chosen first. The formula:
Position size = risk amount ÷ (stop distance × pip value per lot)
Worked example: a $5,000 USD account targeting 1% risk per trade ($50) on EUR/USD with a 25-pip stop-loss. Position size = $50 ÷ (25 × $10) = 0.20 lots, or 2 mini lots.
The same calculation gives different sizes for different stop distances. A 50-pip stop on the same risk parameters gives 0.10 lots. A 10-pip stop gives 0.50 lots. Lot size is the variable that adjusts; account risk percentage and stop distance are the inputs that drive it.
Practical lot-size choices on small accounts
Small accounts run into a floor when the calculated position size falls below the broker's minimum lot increment. A $1,000 account at 1% risk per trade ($10) on EUR/USD with a 30-pip stop requires position size = $10 ÷ (30 × $10) = 0.033 lots — slightly more than 0.03 lots.
On a broker offering 0.01-lot increments only, the trader rounds down to 0.03 lots — risking $9 per trade ($10/pip × 0.03 lot × 30 pips), slightly under the 1% target. On a broker offering 0.001-lot increments, the trader sizes at 0.033 lots and hits the target precisely.
When the calculated size falls below 0.01 lots — for example a $200 account at 1% with a 50-pip stop ($2 risk ÷ ($10 × 50) = 0.004 lots) — the trade is mathematically not viable at the chosen risk percentage on a micro-lot-only broker. The choice is to widen the risk percentage, take a wider stop, or trade on a nano-lot broker.
Why standardised lot sizes exist
The standard-lot convention dates to interbank forex, where currency was traded in $1 million units. The retail-accessible standard lot of 100,000 base currency units was a tenth of that wholesale denomination, kept consistent so that brokers could clear positions through interbank channels.
Mini, micro, and nano lots emerged as retail brokers extended access to smaller traders. They are simply the same standard lot divided by 10, 100, or 1,000. The math is unchanged at every scale; only the absolute size of the position differs. The convention is administrative, not mechanical — but it is universal across retail forex, and platforms expect lot fractions in the 0.01–10.00 range as the typical retail input.