Tick size is the smallest permitted price increment in which a particular futures or options contract can trade. Exchanges specify it in the contract terms, commonly as the minimum price fluctuation or minimum price increment. It defines the contract’s price grid: if the tick size is 0.25 index points, executable prices normally move in 0.25-point steps rather than arbitrary decimals.
Tick size is not tick value
Tick size is expressed in the contract’s quoted price units; tick value is the monetary change in contract value associated with a one-tick move in one contract. For many linear futures contracts, tick value can be derived by multiplying the tick size by the monetary value of one quoted price unit, although the exact calculation depends on the contract’s quotation convention. Two contracts can therefore share the same tick size but have different tick values because their multipliers or units differ.
The distinction matters because a one-tick bid-ask spread is not equally expensive across products. Order-book price resolution is governed by tick size, while the cash impact of moving one price increment is governed by tick value. A finer tick permits more granular quoting, but it does not by itself guarantee tighter effective spreads or greater liquidity.
The minimum can be conditional
A common simplification is to treat each contract as having one permanent tick size. Exchange rules can be more specific. The minimum increment may differ by transaction type, spread structure, option premium level, or proximity to expiration, and exchanges may amend it over time. Researchers should therefore use the specification applicable to the instrument, trading method and historical date being studied rather than hard-code a timeless constant.
This becomes important in backtesting and execution models. If the permitted price grid changed, applying today’s tick to older data can admit prices that were not executable at the time or exclude prices that were, distort slippage assumptions or misstate the smallest possible mark-to-market change. Tick size is therefore both a contract specification and a market-microstructure constraint. It tells you how finely prices may be expressed; it does not measure the contract’s notional exposure, predict price direction or cap the market’s total move.