What Is Lot Size in F&O and How It Is Decided

Short answer: A lot is the fixed minimum quantity of the underlying that one futures or options contract represents; the exchange sets and periodically revises lot sizes so each contract has a standardised, reasonable value.

What a Lot Means

In the derivatives market you cannot trade a single share of an underlying; you trade in lots. One contract equals one lot, and the lot size tells you how many units of the underlying (shares or index units) that contract controls. Your exposure is the lot size times the price.

Who Sets It

The exchange, under SEBI's framework, decides the lot size for each stock and index derivative. They aim to keep the contract value within a target range, so that contracts are neither too small to be efficient nor too large to be inaccessible.

Why Lot Sizes Change

As the price of an underlying rises or falls significantly over time, the exchange revises the lot size to keep the contract value reasonable. If a stock's price climbs sharply, the lot size may be reduced; if it falls, the lot size may be increased.

Impact on Capital Required

Lot size directly affects how much money you need. For futures, your margin is based on the contract value, which depends on lot size. For option buyers, the premium you pay is per unit multiplied by the lot size, so even a small premium can mean a meaningful total cost.

Index vs Stock Lots

Index derivatives and stock derivatives have different lot sizes, and these differ across stocks too. Always check the current lot size before trading, since trading even one contract can represent a large rupee exposure.

Practical Tip

Because lots fix your minimum trade size, F&O often requires more capital and risk per trade than buying a few shares. Confirm the lot size and resulting exposure, and size your positions so a single contract does not overweight your account.

This explainer was written by The Dispatch desk to answer a question readers commonly ask. It is general information, not personalised financial advice.