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Start Learning → Browse All Articles →F&O lot size is the fixed quantity of the underlying instrument bundled into a single futures or options contract, set by the exchange rather than chosen freely by the trader placing an order. Every contract on a given underlying trades in multiples of this one fixed quantity, which means the lot size directly determines the smallest possible position size and the smallest possible increment by which that position can be increased or reduced. This piece works through how lot size is actually set, why it gets revised periodically, how those revisions affect a trader’s existing positions and long-term price charts, and the practical habits worth building around tracking it.
A futures or options contract is never traded in single shares or single units of the underlying commodity; it is always traded in a fixed bundle called a lot, and the lot size specifies exactly how many units of the underlying that one contract represents. Placing an order for one contract is placing an order for that entire bundled quantity at once, not for a single unit of whatever the contract references.
This matters immediately for position sizing, because a trader cannot buy or sell a fraction of a lot, and every order must be placed in whole-lot multiples. A trader wanting exposure smaller than a single full lot simply cannot achieve that in the derivatives segment for that instrument; the lot size sets a hard floor on how small a derivatives position in that underlying can be.
The concept applies identically whether the underlying is an equity index, an individual stock, or a commodity, even though the actual quantity bundled into a lot varies enormously across these categories. A single index contract represents a notional exposure calculated from the index level multiplied by the lot size, a single stock futures contract represents a specific number of shares of that company, and a single commodity contract represents a specific weight or volume of that commodity. In every case, though, the underlying principle is identical: one contract equals one fixed, exchange-defined bundle, never an arbitrary amount chosen by the two parties to the trade.
Lot size is set by the exchange with the goal of keeping the value of a single contract within a reasonably consistent range relative to prevailing prices, rather than letting contract value drift arbitrarily as the underlying price moves over time. A lower-priced underlying is generally assigned a larger lot size, and a higher-priced underlying a smaller one, so that the total value represented by a single contract stays in a broadly comparable band across different instruments.
Keeping contract values in a broadly similar range makes the overall derivatives market easier to standardise and risk-manage, since margin requirements, position limits and other risk controls are all built around contracts of a roughly comparable scale. If lot sizes were never adjusted, a stock or index that rose substantially over the years would eventually carry a contract value many times larger than when the lot size was originally set, distorting the comparability that the exchange is trying to maintain across the market.
There is also a practical accessibility consideration behind keeping contract value within a target range. If a lot size were left unadjusted while the underlying’s price rose steadily over several years, the capital required to hold even a single contract would eventually climb well beyond what a large share of active participants could comfortably commit, effectively shrinking the pool of traders able to access that contract at all. Periodic downward revision keeps a single contract within reach of a broader base of participants even as the underlying itself becomes more expensive over time, which supports liquidity in the contract rather than letting it concentrate among only the largest accounts.
Because the underlying price of a stock or index moves continuously while the lot size stays fixed until deliberately changed, the exchange periodically reviews and revises lot sizes to keep contract values within its target range. A sustained rise in an underlying’s price over an extended period is the most common trigger for a downward revision in lot size, while a sustained decline can occasionally trigger the opposite adjustment.
These revisions are not tied to a fixed calendar and do not happen on every contract at once; they are reviewed periodically across the exchange’s full list of eligible underlyings, with individual instruments revised as and when their contract value drifts far enough from the target range to warrant a change. This means a trader cannot assume lot size for a given underlying is static indefinitely, even if it has not changed for a long stretch of time.
A corporate action on an individual stock, such as a bonus issue or a stock split, is another distinct trigger for a lot size adjustment, separate from the ordinary price-drift review described above. When the number of outstanding shares changes through such an action, the exchange typically adjusts the lot size for that stock’s derivatives contracts in proportion, so that the total value represented by a contract remains broadly consistent with what it was immediately before the corporate action, rather than being distorted purely by an accounting-driven change in share count.
When a lot size changes, it takes effect from a specified future contract cycle, generally applied prospectively to new contracts rather than retroactively altered on positions already open in an expiring series. A trader holding a position in the old lot size going into expiry settles that position under the terms it was originally opened with, and any new position opened from that point forward in a later expiry uses the revised lot size.
The practical effect of a revision is that the same number of contracts before and after a change can represent a meaningfully different total exposure, since the quantity bundled into each contract has itself changed. A trader who mechanically opens the same number of contracts in the new series as they habitually did in the old one, without checking the revised lot size, can end up with a materially different position size and margin requirement than intended, purely from not updating that one input.
Lot size revisions also have a quieter effect worth knowing about: any chart or dataset that expresses volume or open interest in terms of the number of contracts, rather than the number of underlying units, becomes harder to compare across a period spanning a lot size change. A given number of contracts traded before a revision does not represent the same total quantity of the underlying as that same number of contracts traded after the revision.
Anyone doing longer-term analysis of open interest or contract volume trends for an underlying that has gone through a lot size revision needs to account for this discontinuity rather than reading a raw contracts-traded figure as directly comparable across the change. Converting contract-based figures into underlying-unit terms, where the data allows it, removes this distortion and gives a genuinely comparable series across the revision.
This is easy to overlook because the discontinuity does not announce itself visually on a typical contracts-based chart; the line simply continues, and nothing in the chart itself flags that the meaning of a single unit along that line changed partway through. Anyone building or reading a long-running open interest series worth trusting needs to actively check the underlying’s lot size history rather than assume the chart’s own continuity is a guarantee that the underlying measurement stayed consistent throughout.
The exchange publishes current lot sizes for every eligible futures and options underlying as part of its regular contract specifications, and this published list is the authoritative source to check rather than relying on a figure remembered from an earlier period or seen on an older reference page. Trading platforms generally display the current lot size directly on the order entry screen for a contract, which is the most convenient point to confirm it before placing an order.
A simple habit worth building is checking lot size explicitly whenever returning to trade an underlying after a gap of some months, rather than assuming it has stayed the same as the last time a position was taken. This single check avoids the most common and avoidable mistake tied to lot size revisions: sizing a new position based on an outdated figure.
It is also worth watching for any advance notice the exchange typically issues before a lot size revision takes effect, since these changes are announced ahead of the contract cycle they apply to rather than being sprung on the market without warning. Reading these circulars, or a summary of them, gives a trader time to plan the transition to a new lot size deliberately rather than discovering the change only when placing an order in the newly revised contract for the first time.
Lot size is set independently for each underlying and each segment, meaning an equity index, an individual stock, and a commodity each have their own lot size determined by their own price level and the exchange’s own review process for that segment. There is no single rule of thumb that applies uniformly across equities, indices and commodities, since each segment’s underlying instruments carry entirely different price levels and volatility characteristics.
Commodity lot sizes are typically expressed in physical measurement units relevant to that commodity, such as a fixed weight or volume, rather than being derived purely from a price-value target the way equity and index lot sizes broadly are. This reflects the practical trading and, in some cases, delivery conventions specific to that commodity’s own market, which is a separate consideration from the equity-market logic of keeping contract value in a target range.
Because of this, comparing lot size conventions directly across an equity index contract and a commodity contract is rarely a meaningful exercise on its own. What is genuinely useful is checking, for whichever specific underlying is actually being traded, both the current lot size and the total notional exposure that one contract represents at prevailing prices, since that combination is what actually determines position size and margin, far more than the raw lot size figure viewed in isolation ever could.
It is the fixed quantity of the underlying instrument bundled into one futures or options contract, set by the exchange. Contracts trade only in whole multiples of this quantity, not in single units of the underlying.
The exchange periodically revises lot size to keep the total value represented by one contract within a broadly consistent range as the underlying’s price moves over an extended period, most often after a sustained rise or fall.
A revision generally applies to new contract cycles going forward. A position already open in an expiring series settles under the lot size it was originally opened with.
The exchange’s published contract specifications are the authoritative source, and most trading platforms also display the current lot size directly on the order entry screen for that contract.
No. Each underlying and segment has its own lot size, set independently based on that instrument’s own price level, volatility, and, for commodities, its physical measurement conventions.