What an order book is and why to look at it
An order book is the list of every order on a coin right now: who is willing to buy how much, and who is willing to sell how much.
It answers one practical question: how much will I actually get at that price. The price you see on any screen is the best order. Two hundred dollars may sit behind it, or two hundred thousand. That difference decides everything.
How it is arranged
Each line is somebody order: a price and a size. Buy orders run down from the highest price, sell orders up from the lowest. The top line on each side is the "best price".
When you buy at market, your order eats the best sell offers from the top down until it fills. If your size exceeds the first line, part of it fills higher — that is slippage.
When you place a limit order, you join the book and wait for someone to come to you. Filling is not guaranteed, but the price is yours.
Depth: the word that matters
Depth is how much money sits in the book near the current price. A deep book absorbs a large order without moving; a thin one moves by percent.
A simple test: see how much it takes to move the price by 1%. If a couple of thousand dollars does it, the market is thin and your trade will be visible in it.
Our order books section shows the queue across venues side by side, so you can see where your order would land on each.
Why this matters for arbitrage
A scanner shows the best price. If the size behind it is smaller than your capital, the route will not execute the way it looks.
In numbers: a 2% spread, you arrive with a thousand dollars. Two hundred is available at the best price, the rest is 1.5% worse. Two hundred fills well, eight hundred fills with almost no spread, and the average result is about 0.7% instead of 2%.
So the order of operations is: spot the route, check the depth, then open the exchange.
What to check before trading
- Size in the top lines — enough for your amount.
- The gap between buy and sell — the cost of entering and leaving.
- Whether there is a wall — one huge order with a very different price behind it.
- Symmetry. If one side is much heavier, the price will more likely go that way.
Worth remembering
A book is a snapshot of this second. Orders are placed and pulled constantly, and a large one can vanish exactly when you decide to take it. On thin pairs that is routine.
Separately: P2P has no order book in the exchange sense — it is a noticeboard where each advert is its own trade with its own limits. But the logic is the same: read the size, not only the price.
Frequently asked
Why did my order fill worse than I saw? Your size was bigger than what sat at the best price.
Market order or limit order? A market order fills for certain but at a worse price. A limit order gives your price but may not fill. On thin pairs, limit is almost always better.
What is a wall? A very large order at one level. It holds the price while it stands and can be pulled at any moment.