In F&O, the lot size is the fixed, exchange-set quantity that one contract represents. You can trade one lot or several, never half a lot or 17 loose shares. Contract value is that lot size multiplied by the price, and it is the real size of the position you're taking, regardless of the smaller margin you pay upfront.
Why can't I just buy one share's worth?
In the equity segment you can buy a single share. The derivatives segment works in standard packets instead. When the exchange lists a contract on a stock or index, it fixes how many units one contract covers. That's the lot size. Standard packets keep contracts uniform so any buyer's contract exactly matches any seller's; this standardisation is a core feature of the segment, as explained in What is F&O (Futures and Options)?
Lot sizes differ from stock to stock and index to index. They are set (and periodically revised) by exchanges under a regulatory framework that keeps each contract's value within a prescribed band. When a stock's price moves a lot, its lot size can be changed for newly listed contract months. So never assume last year's lot size still applies; check the contract before trading.
How do I calculate contract value? A worked example
Kavita wants to trade Himalaya Agro futures. The details:
- Futures price: ₹400 per share
- Lot size: 500 shares
Contract value = price × lot size = ₹400 × 500 = ₹2,00,000.
One lot commits Kavita to a two-lakh-rupee position. She won't pay ₹2,00,000 upfront, her broker collects a margin, a fraction of the contract value, as a deposit. Suppose that margin works out to ₹40,000 (illustrative). Every ₹1 move in the futures price now changes her P&L by ₹500 (₹1 × lot size). A ₹20 adverse move costs ₹10,000 (a quarter of her margin) even though the price moved only 5%.
That gap between margin paid and exposure taken is leverage, and it's why lot-based products punish casual sizing. Kavita isn't risking "₹40,000 of stock"; she's exposed to a ₹2,00,000 position.
For options, the same multiplication applies to the premium: buying a Himalaya Agro option quoting ₹9 with a lot size of 500 costs ₹9 × 500 = ₹4,500. Option quotes always look small until you multiply by the lot.
How do lot size, margin and exposure compare?
| Term | What it means | In Kavita's trade |
|---|---|---|
| Lot size | Fixed quantity per contract | 500 shares |
| Contract value | Price × lot size. Your true exposure | ₹2,00,000 |
| Margin | Upfront deposit your broker collects | A fraction of ₹2,00,000 |
| P&L per ₹1 move | ₹1 × lot size | ₹500 |
Things to keep in mind
- Judge every F&O trade by its contract value, not the margin. That's the exposure your P&L actually rides on. Leverage cuts both ways; see What are the risks of trading Futures and Options (F&O)?
- Lot sizes are exchange-set and revised from time to time. Check the current lot on the contract before placing an order.
- Multiply every option premium by the lot size to know your real outlay before you tap buy.
- All prices, lot sizes and margin figures above are illustrative, not current contract specifications.
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