Lot size is the standardized unit of trade size in forex. A standard lot is 100,000 units of the base currency. A mini lot is 10,000 units, a micro lot is 1,000 units, and a nano lot is 100 units. When you place a buy or sell order, you express the size as a multiple of these units — for example, 0.50 lots means half a standard lot, or 50,000 units of the base currency.
Lot size determines two things at once: how much currency exposure you carry, and how much each pip of price movement is worth in your account currency. Brokers usually accept fractional lot sizes down to 0.01 (one micro lot), and some allow 0.001 (one nano lot) for fine-grained risk control on small accounts.
Formula
Notional exposure = Lot size in lots x 100,000 x base currency
Pip value (USD-quoted pair) = Lot size in lots x $10
For pairs where USD is the base currency (e.g. USD/JPY), pip value depends on the current exchange rate.
Worked example
You buy 0.30 lots of EUR/USD at 1.0850.
- Notional exposure: 0.30 x 100,000 = 30,000 EUR
- Pip value: 0.30 x $10 = $3.00 per pip
- Price moves up 25 pips to 1.0875: profit = 25 x $3.00 = $75
- Price moves down 25 pips to 1.0825: loss = 25 x $3.00 = $75
Why it matters
Lot size is the lever that converts a chart idea into account risk. Get it wrong and a perfectly correct trade thesis still blows up the account. Every position sizing calculation ends with a lot size — it is the output of the discipline.
Common pitfalls
- Confusing 1 lot with 1 unit — 1 lot is 100,000 units, not one.
- Forgetting that JPY pairs use 0.01 as a pip, not 0.0001 — pip value math is different.
- Using the same lot size on every trade regardless of stop distance, which silently varies risk by 5x or more across setups.