Depth of Market (DOM)
Also known as: order book, level II, market depth
What is it?
Depth of market, often shown as a DOM window or order book, is a live list of the buy and sell orders waiting at each price level around the current market price. Instead of seeing only the single best bid and ask, you see a ladder: how much size people are willing to buy at each price below the market, and how much they are willing to sell at each price above it. This tells you where the liquidity sits and how much size the market can absorb before price has to move. Picture a stack with the current price in the middle, a queue of buy orders building up beneath it, and a queue of sell orders stacked above it.
If the sell side just above price is thin, a large buy order will eat through those small amounts and have to reach up to higher levels to fill completely, which means slippage and possibly a partial fill. If the book is deep and full, a large order can fill cleanly at nearly one price. For a trader, depth is mainly useful when placing larger orders or trading thinner instruments, where it helps you anticipate slippage and partial fills before you commit. You can use it to split a big order into pieces the book can absorb, rather than walking the price against yourself.
One important caution: the book is only a snapshot. Orders can be added or pulled in an instant, so displayed depth is a guide to likely liquidity, not a guarantee of what you will actually get when you trade.
Why it matters: Depth reveals how much size the market can absorb, helping you anticipate slippage and partial fills before you trade.
Reading depth helps anticipate fill quality, mainly relevant on larger sizes or thinner instruments.
Real-world example
Thin depth above price warns that a large buy will slip through several levels rather than filling at one.
How SignalBots handles it
On platforms that expose it (e.g. MT5/cTrader), depth informs how SignalBots-driven orders may fill on larger sizes.
Pro tip
Use depth to size into liquidity - splitting a large order when the book is thin avoids walking the price against yourself.
Common pitfalls
Treating displayed depth as guaranteed; orders can be pulled instantly, so the book is a snapshot, not a promise.
Frequently asked questions
Is depth of market useful for retail traders?
Mostly on larger orders or thin instruments, where it helps you anticipate slippage and partial fills. For small forex trades its impact is limited, because such trades rarely consume enough liquidity to move price.
What does a thin order book tell me?
That little size is waiting at the prices near the market, so a larger order will have to reach across several levels to fill, causing slippage or a partial fill. Deep books, by contrast, can absorb size with much cleaner fills.
Can I trust the numbers shown in the DOM?
Treat them as a snapshot, not a promise. Orders can be added or cancelled instantly, so the displayed depth shows likely liquidity at a moment in time, not a guarantee of what you will actually fill against.
Do all platforms show depth of market?
No. It depends on the platform and the instrument. Some platforms such as MT5 or cTrader expose depth where the broker provides it, while others show only the best bid and ask. Centralised exchanges typically show fuller books than aggregated retail feeds.
How does depth relate to slippage?
Directly. Slippage happens when your order is bigger than the size available at your price, so it fills across deeper levels. Reading the depth before you trade lets you anticipate that and, if needed, split the order to reduce the slippage.