KARACHI: Placing an order on the Pakistan Stock Exchange looks simple — name a share, a price and a quantity — until the terminal starts asking questions that expose a hidden layer of market design. Why must the quantity be a multiple of 500? Why will the price field accept paisas but not fractions of a paisa? Why did a slightly different quantity get routed to a different market entirely? The answers are two of the oldest pieces of plumbing in organised trading: the marketable lot, the standard parcel size in which a share trades, and the tick size, the smallest amount by which its price may move. Neither appears in annual reports or earnings calls, yet together they shape the cost of every trade, the shape of every order book and the feasibility of every small investor's plans. This guide explains both mechanisms, how the PSX sets them, how they interact with order types and circuit breakers, and the practical habits that keep them from quietly taxing your trading.
The marketable lot: shares are sold in parcels
A marketable lot — also called a board lot or simply "the lot" — is the standard quantity of a security in which orders are placed in the regular market. Your order quantity must be a whole number of lots: if a company's lot is 500 shares, you may buy 500, 1,000 or 50,000, but an order for 300 or 750 does not belong in the ready market at all — the 300 is an odd quantity, and the odd remainder routes to the odd-lot segment described in our guide to the odd-lot market. The lot system is a survival from the era of physical delivery, when standardised parcels made counting, delivering and settling share certificates manageable; in the dematerialised CDC era its original purpose has faded, but standard quantities still serve matching efficiency and orderly books, and the lot remains a fact of PSX trading life.
Lot sizes are set per security by the exchange and have historically been scaled to the share's price: the classic schedule assigned large lots to cheap shares and small lots to expensive ones — hundreds of shares for a low-priced stock, stepping down through smaller parcels as the price rose, so that one lot represented a roughly comparable amount of money across the board. The principle survives whatever the current schedule's exact bands: a lot of a share priced in single rupees contains many shares, a lot of a share priced in the thousands contains few, and the exchange reviews and revises lots as prices migrate, notifying changes in advance. The operational rule for the investor never changes: the lot for the share you are trading is displayed in the market data and enforced by your broker's terminal, and it is a number to check, not to assume — particularly after large price moves, splits or consolidations, when lots are reset.
What the lot does to your money
The lot's real significance is the minimum ticket. Multiply lot by price and you have the smallest sum that buys one standard parcel in the ready market. For an inexpensive share the ticket is trivial; for an expensive share with even a small lot it can be substantial — and for Pakistan's famously high-priced shares, a single lot can run into sums that exclude small accounts from the ready market entirely, leaving the odd-lot segment as their only door. Portfolio construction bends around this: equal-weighting a basket of companies is arithmetically impossible when one name's minimum parcel is a large fraction of the portfolio, and position sizing in small accounts is often dictated less by conviction than by which lots fit. This is one of the quiet structural facts behind the popularity of mutual funds and ETFs among small savers — the fund aggregates money until lot sizes stop mattering, a theme our guide to PSX ETFs develops.
The lot also shapes corporate-action outcomes. Bonus and rights entitlements are computed on holdings, not on lots, so they routinely manufacture odd quantities — a 10 per cent bonus on three lots of 500 delivers 150 extra shares, an odd lot riding on a marketable base — and the investor's tidying choices afterward are the subject of the odd-lot guide linked above. Splits and consolidations, conversely, are often used by companies partly to re-tune the lot economics of their shares: adjust the unit count so the price, and therefore the ticket, lands where the company wants its shareholder base to be.
The tick size: the smallest step a price can take
If the lot standardises quantity, the tick standardises price. The tick size is the minimum increment by which the price of a security may change or an order may be priced — on the PSX, prices are quoted to the paisa, and a bid or offer must sit on the grid of permitted price steps rather than at any arbitrary figure. You cannot bid Rs 10.005 for a share; the grid does not have that square. The tick is why order books show queues of orders stacked at discrete price levels, and why "improving" a bid means stepping up by at least one tick to stand ahead of the orders already waiting — the price-time priority mechanics our guide to order matching explains.
Why restrict prices to a grid at all? Because without one, priority becomes meaningless: a rival could jump the queue by an infinitesimal fraction, spreads would collapse into noise, and the incentive to post visible orders — the liquidity the whole market relies on — would evaporate. Tick size is thus a balance struck by the exchange: fine enough that prices can track value closely and spreads can be tight, coarse enough that each price level carries meaningful quantity and queueing for priority is worthwhile. The balance bites differently at different prices. One paisa on a Rs 5 share is a fifth of one per cent — a coarse step that forces spreads wide in percentage terms. One paisa on a Rs 3,000 share is a rounding error, economically invisible. This asymmetry is a permanent feature of low-priced shares everywhere, and part of why the cheapest stocks on the board are not necessarily the cheapest to trade: their minimum spread, set by the tick, is proportionally the largest on the exchange.
Lots, ticks and the rules around them
The two mechanisms interact with the rest of the trading rulebook in ways worth knowing. Circuit breakers — the daily price limits that halt a share's rise or fall at the exchange's prescribed band around the previous close, subject also to an absolute rupee floor for very low-priced shares — are enforced on the tick grid, so limit prices are always tradeable prices. Order types respect the lot: market and limit orders in the ready market are lot-denominated, as our guide to trading sessions and order types sets out, and special instructions like all-or-none are built on lot quantities. The pre-open and closing procedures, the odd-lot segment's acceptance of sub-lot quantities, and the negotiated-deal segment's freedom from lot logic each mark a boundary where the standard parcel gives way to a different mechanism for a different job — a map of the exchange that becomes intuitive once the lot and the tick are understood as the ready market's default settings rather than universal laws.
Practical habits the plumbing rewards
None of this requires strategy so much as housekeeping. Check the lot before sizing an order, especially in an unfamiliar name, and build the minimum ticket into any plan for a small account rather than discovering it at the terminal. Price limit orders on the grid deliberately: a bid one tick above a crowded level buys queue priority for a paisa, often the cheapest immediacy available, while a bid placed at the tail of a huge same-price queue is a hope, not a plan. In low-priced shares, respect the tick's percentage weight — a one-tick spread there costs more, proportionally, than a wide-looking spread in a high-priced name, and churning cheap shares pays that toll on every round trip. When a corporate action leaves you with odd quantities, handle them through the odd-lot route with limit orders rather than forcing them into the ready market. And when a broker's screen shows an unfamiliar lot or a price field that rejects your figure, read it as the plumbing introducing itself — two minutes spent understanding the parcel and the grid will save repeated small costs for as long as you trade. This article is educational content, not financial advice.
How lots and ticks have changed — and why they may change again
Neither mechanism is a law of nature; both are settings, and Pakistan's settings have a history that illuminates their purpose. In the paper era, lots were large because certificates were physical and parcels had to be worth the clerks' time. Dematerialisation through the CDC removed that logic, and in 2009 the Karachi exchange went to the logical extreme, reducing the marketable lot to a single share and standing down the separate odd-lot market altogether — an experiment in radical simplicity. The market's considered judgement, reflected in the framework investors trade under today, settled at a middle position: standardised lots retained for the ready market, with the odd-lot segment restored as the release valve — a verdict that a visible queue of round parcels organises a book better than a free-for-all of fragments, provided the fragments have somewhere honourable to go. Tick sizes tell a parallel story of compression: as systems decimalised and screens replaced chalk, price steps shrank from fractions like the old eighth-of-a-rupee conventions of the region's floor era to the paisa grid of today's terminals, each compression tightening spreads and each generating the same debate — liquidity gained against queue discipline lost — that the previous section described.
The direction of travel worldwide is toward smaller lots and finer ticks as automation cheapens, and toward structures — single-share lots, extended fractional trading in some markets — that dissolve the parcel problem entirely. Pakistan's own experimentation shows the exchange is not doctrinaire about either setting; lots are reviewed and revised by notification as prices and market structure evolve. The investor's interest in the question is practical rather than nostalgic: any future reduction in lot sizes lowers minimum tickets and admits smaller accounts to more of the board, any refinement of ticks tightens the cost of immediacy, and both changes would arrive the same way past ones did — a notice, a revised table, and a morning on which the terminal quietly accepts quantities and prices it rejected the day before. Reading those notices, as with so much of the exchange's plumbing, is a habit that pays out of proportion to its effort.
A worked miniature makes the pair concrete. Take two shares: one priced at Rs 8 with a lot of 500, and one priced at Rs 800 with a lot of 50. The minimum ready-market tickets are Rs 4,000 and Rs 40,000 respectively — the lot table has roughly equalised the effort of participation at the bottom while keeping the expensive share's ticket meaningful. Now watch the ticks: a one-paisa step in the first share is an eighth of a per cent of its value, so its tightest possible quoted spread already costs an eighth of a per cent to cross; in the second share the same paisa is a thousandth of the value, and the spread can tighten to near-invisibility. Same exchange, same rules, opposite trading textures — and both predictable in advance from two numbers printed in the market data, before a rupee is committed.
Key takeaway: The marketable lot fixes the parcel size your ready-market order must be built from, and the tick size fixes the smallest step its price may take — together they set your minimum ticket, your queue position and, in low-priced shares, a proportionally heavy cost of trading that no analysis can wish away.
