Forex & EA basics
XAUUSD Contract Size, Tick Value and Lot Size Explained
Before testing an XAUUSD EA, read the exact broker symbol's contract size, tick size, tick value and allowed volume. “Gold” and “0.01 lots” do not define identical exposure across every account. Broker specifications, not a generic online calculator, are the starting point.
Find the actual contract
In MT5 Market Watch, open the symbol's Specification. Record the symbol name including any suffix, account currency and relevant trading conditions. MetaTrader's Market Watch guide explains access to contract specifications.
Take a dated note for the account used in your test. A screenshot from another broker or account type is not evidence of your own contract. If a required field is unclear, obtain its meaning from the broker before interpreting a position-size calculation.
Do not interchange these units
| Term | What to establish |
|---|---|
| Contract size | The quantity represented by one lot. |
| Point | The platform's symbol point unit. |
| Tick size | The minimum price increment. |
| Tick value | The money value associated with a tick for the specified volume and currency context. |
| Volume step | The permitted increment between valid order sizes. |
These are separate properties in the MQL5 symbol reference. Tick size need not equal point size. When an EA asks for “distance”, find out which unit the input expects.
A conditional gold example
Assume, only for this example, a linear USD-quoted gold contract with 100 troy ounces per lot, a 0.10-lot position and a $5-per-ounce price move. The gross change in position value would be 100 × 0.10 × $5 = $50. The sign depends on the trade direction and price movement.
If the contract instead represented 10 ounces per lot, the same lot number and price move would produce $5. That is why copying someone else's lot setting can copy a number without copying the exposure. These figures exclude costs and are not a recommended trade size.
Use the platform's calculation model
For development, OrderCalcProfit estimates profit or loss for supplied prices and volume in the account currency. OrderCalcMargin estimates margin for a proposed operation. Treat the results as estimates within the current environment, not promises about the eventual fill.
Margin is not a maximum-loss figure. A stop also does not establish an absolute loss ceiling when execution differs from the requested price. Keep price risk, trading costs and margin requirements as separate lines in your worksheet.
Check the EA's units before its return
Compare the input descriptions with the contract: fixed lot, stop distance, spread threshold and any money-based limit. Verify that submitted volume follows the minimum and step, and inspect the resulting values in a demo or historical test.
For a first comparison, keep the source release and inputs fixed and document the contract on each account. Then use the spread and execution-cost guide to understand the remaining differences.
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