What is Level 2 market data, and is it worth paying for? We measured 35 million quotes

Level 2 market data shows you the order book: not just the best bid and offer, but the resting orders behind them, level by level. Brokers charge for it, and the usual advice is either "you need it" or "it is noise". Both answers are given without numbers. So here are the numbers. We recorded ten levels of book on every quote for 264 US trading sessions — 35,207,932 quotes — and measured what the ladder actually holds. The short version: the price you see on Level 1 is good for about $1,155 to $5,150 depending on the stock, and the entire visible ten-level ladder holds $35,000 to $84,000. If you trade smaller than the first number, Level 2 will rarely change a decision. If you trade near or above it, Level 1 is actively misleading you.

1. What Level 1 and Level 2 actually show

Level 1 is the top of the book: the best bid, the best offer, and the size available at each. Every broker gives you this. It answers "what is the price right now". Level 2 adds the levels behind the touch — the resting orders at the next best prices, on both sides. It answers a different question: "how much can I trade before the price I get gets worse". That second question is the one that decides whether an order fills where you expected. And you cannot answer it from Level 1, because Level 1 shows one number and hides the shape.

2. What the quoted price is actually worth

For every quote in the archive we filled a market buy against the recorded ask ladder, level by level, and found the largest order whose average fill stayed within a given distance of the best offer. Medians, regular trading hours only. Read the first column as the honest size of the quoted price. A $2 stock displays a price that is good for about $1,155. A $50 stock displays one good for about $5,150. The rest of the table is where Level 2 earns its keep, because the three rows behave completely differently once you allow yourself to pay slightly more. In the $20-200 band, accepting 10 basis points above the touch multiplies your size four and a half times, from $5,150 to $22,977. The levels are close together, so a small concession buys a lot of room. In the $1-5 band, the same 10 basis points buys almost nothing — $1,299 against $1,155. The minimum tick is a cent, so on a $2 stock one tick is already 50 basis points. There is no gentle slope to walk up. You are either at the touch or you have jumped a long way. That difference is invisible on Level 1. Both stocks show you a price and a size. Only the ladder tells you which one you can lean on.

3. Ten levels is not very much money

The whole visible ladder holds between about $35,000 and $84,000 on a typical quote. That is everything ten levels can see, and it is not a large amount of money. Two things follow that matter more than they sound. The best price is a small slice of the book. Between 3.9% and 6.3% of ten-level depth sits at the top level. Roughly 94% of what you can see is behind it, at worse prices. If you size an order off the displayed size at the touch, you are sizing off one twentieth of the visible market. Both sides are similar, with the bid slightly thinner. Bid depth runs 82% to 95% of ask depth. Exits cost about what entries cost, and a little more in cheap names. Strategies are usually sized on the entry with the exit assumed free; it is not free, and it is about the same.

4. The opening half hour is the thinnest part of the day

Largest buy staying within 25bp of the best offer, by time of day. In the $20-200 band the opening half hour supports $32,449 against $45,456 in the early afternoon — about 29% less. The cheaper bands are flatter, but never better at the open than later. Put that next to spreads, which are also widest at the open, and the picture is consistent: at the open you pay more per share and you can trade less of it before you pay even more. The period with the most movement is the period in which it is hardest to act.

5. When Level 2 changes a decision

Level 2 is worth paying for when your order is large enough that the ladder shape matters. From the numbers above, that means roughly: Your order is comparable to top-of-book depth. If you are buying $5,000 of a $3 stock, the best offer holds about $1,155 — you are going to walk the ladder, and you want to see it first. You need to size an exit. Bid depth is 82-95% of ask depth. An exit that assumes the entry's liquidity will be there is assuming something the book can tell you. You trade the open. Depth is about 29% lower in the first half hour in liquid names, and that is exactly when most intraday strategies are active. You trade cheap stocks. In the $1-5 band, one tick is a large percentage, so the difference between resting at the touch and crossing is much bigger than it looks.

6. When it does not

Your orders are small relative to the touch. If you buy $1,000 of a $50 stock, the best offer alone holds around $5,150. You will fill at the quote. Level 2 will confirm that every time, which is another way of saying it tells you nothing you needed. You expect it to predict direction. It shows resting size, not intent. Orders are cancelled, hidden and replaced constantly. Nothing in our measurements suggests visible depth forecasts which way the price goes, and we would be suspicious of anyone claiming otherwise without showing the test. You only have ten levels and your order needs more. Ten levels was not enough to fill a $25,000 order 28.7% of the time. Beyond the visible ladder, Level 2 is silent — it does not tell you what is out there, only that what you can see is not enough.

7. How to get it, and what to check

Most US brokers offer Level 2 as a paid market data subscription. Some include a limited version free. Before paying, check three things. How many levels. Ten is common. Some feeds give five, which given the numbers above is not much of the book at all. Whether it updates or snapshots. A book that refreshes once a second is a different product from one that streams every change, and for anything intraday the difference matters. Whether your platform records it. A live ladder you cannot replay is a ladder you cannot test against. If you are going to size orders on depth, you want the same data available when you backtest on your own recording, otherwise your test is assuming a fill your live book would have refused. The honest summary: Level 2 is not a signal, it is a measurement of how much room you have. Whether that is worth a monthly fee depends entirely on whether your order size is bigger than $1,155.