A "lot" is how much currency you're trading. It's a trivial concept with significant consequences: choose too large, and a normal market swing blows your account; choose too small, and the per-trade cost of spread eats your returns faster than the strategy can generate them. This article explains the lot-size tiers every broker offers and how to pick the right one for your account.
The short answer
In forex, a standard lot is 100,000 units of the base currency. For EUR/USD, one standard lot means you're controlling €100,000 worth of exchange exposure.
Brokers subdivide the standard lot into smaller increments:
| Lot type | Units | Common MT5 volume input | Pip value on EUR/USD |
|---|---|---|---|
| Standard | 100,000 | 1.00 | ~$10 |
| Mini | 10,000 | 0.10 | ~$1 |
| Micro | 1,000 | 0.01 | ~$0.10 |
| Nano | 100 | 0.001 | ~$0.01 |
The MT5 "Volume" field is expressed in standard lots. 0.10 means one mini lot, 0.01 one micro lot. This convention is universal across brokers.
Why these specific numbers
Standard lots come from interbank FX. The smallest practical quote between banks is $1 million. Retail brokers inherited a shrunk version — 100,000 units — as their "standard" while keeping the terminology. Mini, micro, and nano are each 1/10 of the previous tier.
The tier you should use depends on two things: your account size and your per-trade risk.
The position-sizing math
Suppose you have a $5,000 account and want to risk 1% per trade ($50 risk). You have identified a trade with a 20-pip stop-loss.
Pip value needed per pip:
Pip value = Risk / Stop distance in pips
Pip value = $50 / 20 = $2.50 per pip
Now convert pip value to lot size (for USD-quoted pairs):
Lot size = Pip value / $10 per standard lot
Lot size = $2.50 / $10 = 0.25 lots
So you'd enter 0.25 as volume — that's 2.5 mini lots, or 25 micro lots. If your broker supports that precision, you enter 0.25 directly; if not, round down to 0.20 or 0.24 to stay within the risk budget.
This calculation is the entire job of position sizing. Every automated system, including Aurion, does this exact arithmetic before every trade — tailored to the exact account size and stop distance in the moment.
The case for micro lots — and against nano
Micro lots (0.01) are the right default for most retail accounts below $10,000. They give you:
- Risk granularity fine enough to survive small accounts (you can risk $0.50 on a 50-pip move)
- Psychological distance from the screen — a $50 loss on a $5,000 account stings but doesn't traumatize
- Enough pip value that spread cost (0.5 pips × $0.10/pip = $0.05) doesn't dominate
Nano lots (0.001) are almost always a red flag. Brokers that offer nano-lot trading usually fall into one of three categories:
- Education-focused brokers (e.g., OANDA for US retail) that genuinely serve tiny accounts — these are fine but limited in other ways.
- Predatory brokers that advertise nano-lots to attract first-time traders with $50 deposits. The customer support, execution quality, and spreads tend to be poor.
- Shady marketing where "nano lots available" is a headline but nothing below 0.01 actually fills in practice.
If your strategy requires nano-lot precision, your account is too small for that strategy. Size up the account or size down the strategy.
Different asset classes, different lot meanings
Outside FX, "lot" has inconsistent meanings across brokers. Always verify in the contract specifications:
| Instrument | Typical "1 lot" meaning |
|---|---|
| EUR/USD | 100,000 EUR |
| XAU/USD (gold) | 100 troy ounces |
| Oil (WTI) | 1,000 barrels (some brokers 100) |
| Indices (S&P 500) | 1 CFD contract = 1× index value (varies) |
| BTC/USD | 1 BTC (some brokers 0.01 BTC) |
Before trading any new instrument, open MT5's Symbol Specification dialog (right-click in Market Watch → Specification) and check:
- Contract size — what does "1.0 lot" mean in the underlying
- Minimum volume — the smallest lot your broker allows
- Volume step — the increment (usually 0.01)
- Maximum volume — rarely relevant unless you're sizing large
The execution difference between lot sizes
There is no execution penalty for smaller lots on an ECN broker. A 0.01 lot and a 10.0 lot go to the same liquidity pool; both fill at the top-of-book bid or ask.
On market-maker brokers, small lots sometimes get internalized (filled against the broker's book) while large ones get hedged externally. This can lead to tiny differences in slippage between sizes. It's almost never enough to matter for retail accounts.
The one real execution difference is on very large orders: a 50-lot order on a less-liquid pair may walk through multiple levels of the order book, getting a slightly worse average price than a 0.5-lot order. This starts mattering around $5M+ notional — not a concern for retail.
The psychology of lot sizing
A subtle but important effect: the size of a position changes how you trade it. A 0.01-lot trade where $5 is on the line is easy to let run. A 2.00-lot trade where $2,000 is on the line is extremely hard to let run, even if the strategy says to. Your stop-loss discipline erodes as position size grows.
Traders often overestimate how much size they can handle. The test is this: if the worst-case loss on your stop happened right now, would you still be able to objectively take the next signal? If not, your size is too large for your psychology.
This is where automated systems have a genuine edge. An EA doesn't flinch when a 1.5-lot position is $800 in the red. It just waits for the stop or target. For a human, the same trade is orders of magnitude more stressful — and stress compromises decisions.
What to do with this
Three concrete takeaways:
-
Start with micro lots on any new strategy or instrument. Trade 50+ positions at 0.01 before sizing up. The cost of misjudged sizing at 0.10+ is much higher than the opportunity cost of trading small.
-
Calculate lot size from risk, not gut feel. Every trade: what's my risk in dollars? What's my stop distance in pips? Lot size = (risk / stop) / pip value per lot. Make this math automatic before every entry.
-
Check contract specifications for every new instrument. Don't assume. Gold ≠ EUR/USD. Indices ≠ FX pairs. Cryptos have the most variance. Read the spec once when you add the symbol; save yourself a costly surprise later.
Lot size is the lever that translates your strategy into account impact. Get it right and everything else has a chance of working. Get it wrong and even a perfect strategy blows up.
Related reading
- What Is a Pip and a Point? — the unit of price movement
- What Is Position Sizing in Trading? — the full risk-to-lot-size workflow
- What Is Leverage in Trading? — why high leverage enables oversized lots