Lot size

A lot is the standardized trade quantity your broker uses to size a position. In forex, a standard lot is 100,000 units of the base currency, a mini lot is 10,000, and a micro lot is 1,000 — so trading 0.1 lots means 10,000 units, not "a tenth of something vague." Futures use the same idea under a different name: one contract is a fixed block (5,000 bushels of corn, 1,000 barrels of crude), and you trade whole contracts. Equities have round lots of 100 shares, though most retail brokers now fill any share count. The point is the same everywhere: you don't buy an arbitrary amount, you buy a defined, quantized unit.

How it's calculated

Lot size translates into two numbers that matter: notional exposure and money-per-move. Notional is just units times price. One standard lot of EUR/USD at 1.0850 controls 100,000 × 1.0850 = $108,500 of exposure, even though you post only a fraction of that as margin.

The number you actually feel trade-to-trade is money-per-pip. For most USD-quoted forex pairs, a pip is 0.0001 of price, so pip value = lot units × 0.0001.

Work it concretely. You go long 1 mini lot (10,000 units) of EUR/USD. Each pip is worth 10,000 × 0.0001 = $1. Price runs 30 pips in your favor and you make $30; it runs 30 pips against you and you lose $30. Scale to a standard lot and every pip is $10, so the same 30-pip move is ±$300. Futures work identically with ticks instead of pips: one crude contract moves $10 per $0.01 tick, so lot count directly scales your per-tick money.

Why it matters

In forex, choosing a lot size is position sizing — there is no separate step. Once you know your stop distance in pips and your dollar risk, the lot size falls out: risk dollars ÷ (stop pips × pip value per lot). Risk $200 with a 40-pip stop and you can trade 0.5 standard lots ($5/pip), because 40 × $5 = $200. Pick the lot first and ignore the stop, and you've set your risk by accident instead of on purpose.

Lot size also drives margin and, through it, leverage. Bigger lots mean more notional, more margin locked up, and less free margin buffering you against adverse moves — so oversizing quietly pushes you toward a margin call long before your thesis is wrong.

Watch the rounding constraints. Brokers quantize lots to a minimum step, usually 0.01 (a micro lot). You can't trade 0.037 lots; you round to 0.03 or 0.04, and on small accounts that rounding can force you to risk meaningfully more or less than you intended. Size in micro lots when precision matters, and always confirm your broker's minimum before assuming a calculated size is tradeable.

Related concepts

Nail down pip value and margin first — they're the inputs that turn a lot count into real risk. Then let a position size calculator convert your account risk and stop distance into a broker-ready lot size in one step. To see whether your chosen sizes actually match your intended risk over time, log every position in the Tradeways journal and review lot size against outcome.