Lot Size (F&O)
The minimum number of units of an underlying asset that must be traded in a single futures or options contract on NSE, as periodically revised by the exchange to keep contract values within a regulated notional range.
Every futures and options contract on NSE is standardised, and one of the most fundamental parameters of that standardisation is the lot size — the fixed number of shares (or units) that constitute one contract. A trader cannot buy or sell half a lot; the position must always be a whole number multiple of the prescribed lot size.
NSE determined lot sizes so that the notional value of one contract — calculated as lot size multiplied by the current market price of the underlying — fell approximately within a target range of Rs 5 lakh to Rs 10 lakh at the time of introduction. As stock prices changed over time, the exchange periodically revised lot sizes upward or downward to bring the contract value back into this band. SEBI circulars from time to time revised this minimum notional value threshold; in its 2021 circular SEBI raised the minimum contract size to Rs 5 lakh, prompting NSE to recalibrate lot sizes across hundreds of single-stock derivatives.
The lot size is also directly linked to the Market-Wide Position Limit (MWPL) framework. NSE computed the total open interest across all participants in a stock's F&O contracts in terms of number of shares, then compared it to the free-float shares outstanding to arrive at the MWPL utilisation percentage. Because each contract represents a fixed number of shares equal to the lot size, a change in lot size mechanically altered how quickly aggregate open interest approached the MWPL threshold.
For index derivatives such as Nifty 50 and Bank Nifty, lot sizes were set differently. The Nifty 50 lot size was reduced from 75 to 50 units in 2019 and again revised subsequently, while Bank Nifty had its own distinct lot size. These revisions affected the margin required per contract and therefore the capital efficiency available to participants.
Traders needed to factor lot size into position sizing calculations. For example, if a stock traded at Rs 2,000 and the lot size was 300, the notional value per contract was Rs 6 lakh. An option writer collecting premium of Rs 50 per share received Rs 15,000 per lot. Understanding the lot size was therefore prerequisite to interpreting margin requirements, maximum loss on a naked position, and the leverage embedded in any derivative strategy.