Round Lot Jump to the manual 100 shares = 1 lot

A reference on how the machinery works

Market mechanics: options, screening and execution in plain terms

the plumbing between them

Round Lot is a reference on market mechanics, written for people who want to understand how the market mechanically works before they use it: what a contract obliges, what a screening filter actually removes, and what happens between a click and ownership. It never names a security to buy.

bid ask odd lot 53.3553.3053.2553.2053.1553.1053.0553.0052.9552.9052.8552.8052.7552.70
One round lot of 100 shares, the unit a US quote is published in, resting across fourteen price levels, bids left of the price axis and asks right. The three outlined marks below sit outside the lot: an odd lot.
Standard trading unit
100 shares
Settlement cycle
T+1
Axes per platform
5
Terms defined
30
Securities recommended
none

One hundred marks: one round lot, the unit this site is named after. Bids to the left of the midpoint, asks to the right, and the whole page built on the same ten-cell module.

The reference

Where these market mechanics are explained

Worked example

Why break-even is not the strike

35 40 45 50 55 60 65 -5 0 +5 +10 +15 break-even 53 strike 50 profit / loss per share (USD) share price at expiry (USD)
Long call, strike 50, premium 3. The dashed line marks break-even at 53: the strike plus the premium, never the strike alone.

A long call struck at 50 does not turn profitable at 50. The buyer has already paid the premium, so the position starts three dollars down and stays exactly three dollars down for every price below the strike. That is the flat left arm of the diagram, and it is the part most first explanations skip.

Above the strike, intrinsic value climbs one-for-one with the share price. It spends the first three dollars of that climb repaying the premium, which puts break-even at 53, the strike plus what the contract cost. The same arithmetic run backwards gives the writer's diagram: the identical line reflected through the zero axis, which is why a covered call caps its own upside at exactly the point the buyer's begins.

This is the shape of every page here. Take one mechanism, state what it obliges, do the arithmetic in public, and show the figure that falls out of it. The payoff calculator will run the same computation for any strike and premium you give it, including the written side.

Market mechanics rewards this kind of reading. Almost nothing in the machinery is genuinely difficult once the obligation is stated plainly; what makes it feel difficult is that the obligation is usually left out. A page on screening that never says which companies a filter silently removes, or a page on execution that never mentions who your order is actually sold to, has explained the vocabulary and skipped the mechanism.

Platforms

Compared on order types and options approval

Four platforms on five mechanical axes. Feature facts only: no ratings, no ranking, and nothing that implies one of them is the right choice for you.

Illustrative platform data. Commissions are per options contract; order-type counts include conditional and bracket orders.
PlatformOptions / contractOrder typesOptions approvalFractionalMarket data More
Apex One$0.0012Tier 3yesLevel 2
Meridian$0.659Tier 2yesLevel 1
Halyard$1.0014Tier 4noLevel 2
Coastline$0.007Tier 1yesLevel 1

Figures are illustrative and shown to demonstrate the axes, not to rank the platforms. The live comparison lives in the compare tool.

One hundred small square metal type-slugs laid out in a shallow letterpress galley, two facing columns either side of a narrow empty channel, three slugs set apart below

Set by hand. One hundred slugs either side of an empty channel, three set apart below: the same figure the hero draws, in metal.

Vocabulary

Screening, execution and the terms both depend on

Screening pages and execution pages lean on the same small vocabulary, so market mechanics gets defined once and linked from everywhere. Twelve of the most load-bearing terms below, with the rest in the glossary, because understanding how the market mechanically works is mostly a matter of knowing which word means which obligation.

FAQ

What this reference is, and is not

Does Round Lot tell me what to buy?

No, and it never will. Every page here answers a mechanical question: how an order routes, how a premium decays, how a score is computed. There are no recommendations, no price targets and no coverage of individual companies. If you want to know whether to buy something, this is the wrong reference; if you want to know what happens when you do, it is the right one.

Is a round lot still 100 shares?

On the US equity exchanges the standard round lot remains 100 shares for the great majority of listed names, and public quotations are published in round-lot terms. Odd-lot orders are accepted and filled, but historically they were reported separately and did not update the public quote, which is why the distinction still shows up in market data documentation.

Where do the numbers in the examples come from?

They are constructed. Every worked example on the site uses round, invented figures chosen to make the arithmetic legible: a strike at 50 and a premium at 3 rather than 47.82 and 2.61. The arithmetic is real and can be checked; the prices are not quotes and are not meant to resemble any particular security.

How is market mechanics different from investment advice?

Advice tells you what to do with your money. Mechanics tells you what the machinery does with your instruction. A page explaining that a cash-secured put obliges you to buy 100 shares at the strike if assigned is describing a contractual fact. A page telling you that selling that put is a good idea this month is doing something else entirely, and this site does not do it.