Contract size: what it means and how it works

What is contract size

Contract size is the number of units of the underlying asset that a single lot of an instrument represents.

A lot is the unit you use to set trade volume on a platform. The contract size tells you what that lot holds in real terms:

• currency units of the base currency for a forex pair
• troy ounces for gold (XAUUSD)
• barrels for oil
• an amount per index point for indices such as US100 or NAS100

Lot size and contract size

These two terms are often mixed up, but they are different things:

Fractional lots, such as mini and micro lots, are fractions of the same contract. They do not change the contract size.

Worked example (hypothetical)

Use letters instead of real figures, and then put your own values into a calculator:

• C is the contract size of a forex pair, in base-currency units
• L is the number of lots you open
• P is the price of the pair

The calculations are:

• Position size = L × C units of the base currency
• Notional value in the quote currency = L × C × P
• Value of a price move: the change in price × L × C, in the quote currency
• Margin required = notional value ÷ leverage, converted into your account currency

If L doubles, every result doubles. If the contract size is larger on another symbol, the same lot holds more units, so each price move is worth more. This is why the same volume on gold, an index and a currency pair gives very different exposure.

Leveraged forex and CFD trading can lose money fast. A small mistake in units per lot can make a position far larger than you intended.

Where the term appears

• MetaTrader: in MT4 and MT5, right-click a symbol in Market Watch and open its Specification. "Contract size" is listed there next to fields such as digits, tick size and volume limits.
• Broker contract specifications: tables of instruments that list units per lot. Always check the specification for the exact symbol and account you use.
• Exchange futures specifications and news: futures have a fixed contract unit or multiplier. "Mini" and "micro" futures have a smaller contract size than the full contract.
• Reports: an account statement usually shows volume in lots. To get the actual units traded, multiply the volume by the contract size.

Precise definition and edge cases

Formally, contract size is the quantity of the underlying that one contract or lot delivers or references. For cash-settled CFDs and futures, it is the multiplier used to turn a price change into profit or loss. See cash vs physical settlement.

Edge cases to know:

• It differs between brokers. The same index or crypto CFD can have different units per lot at different brokers.
• Cent-type accounts show balances in cents, so values on screen are scaled. Check how the symbol is defined on that account.
• Index CFDs may define a lot as a fixed amount per point, not as a number of "shares" of the index.
• Volume limits are separate from contract size. The minimum volume and the volume step limit what you can enter, but they do not change contract size.
• Futures-based CFDs can roll between contracts. See futures roll and front month.

Related terms

• Trading glossary
• Trading basics
• Risk management
• Currency pairs
• Metals
• Stock indices
• Derivatives
• Expiry date

Frequent questions

What is contract size in forex?

It is the number of base-currency units in a single lot of a currency pair. It is shown in the symbol specification on your platform.

Is contract size the same as lot size?

No. Lot size is how many lots you trade. Contract size is how many units each lot contains.

Is contract size the same for every instrument?

No. It is set per symbol and can differ between asset classes, brokers and account types.

How do I find the contract size on MT5?

Right-click the symbol in Market Watch, choose Specification, and read the "Contract size" field.

Why does contract size matter for risk?

Profit, loss and margin all scale with lots multiplied by contract size. If you misread it, the position can be much larger than you planned.