Depth of market, or DOM, is the order book: a live ladder showing not just the current bid and ask, but how much buyers and sellers are willing to trade at each price around it. Where a normal quote shows one price, the DOM shows the queue behind it — how many lots are waiting to buy just below and sell just above. It is often called Level 2 data, and it tells you how much size the market can absorb before the price has to move.
What it is
A single quote gives you the best bid and best ask — the top of the book. The DOM shows several rungs on each side:
- Bids below, stacked by price, each with the volume waiting to buy there.
- Asks above, stacked by price, each with the volume waiting to sell there.
Read together, they show where liquidity sits. A price with 50 lots resting on it will hold against a small order; a price with 2 lots will give way. The DOM is that map of resting size, updating tick by tick.
How it works
Each side of the book is a queue. When you send a market buy, it fills against the lowest asks first, then the next, then the next, climbing the ladder until your full size is done. If you buy more than the top rung holds, you eat into the rungs above and your average fill price rises — that is slippage, shown before it happens. A large resting order can act as a wall: price stalls there because there is enough size to soak up what hits it. When that order is pulled or filled, price often moves quickly through the gap it leaves.
A worked example
Suppose the EUR/USD DOM shows this near the top:
- Asks — 1.0852: 3 lots · 1.0853: 8 lots · 1.0854: 20 lots.
- Bids — 1.0851: 5 lots · 1.0850: 12 lots · 1.0849: 15 lots.
Send a market buy for 2 lots and you fill at 1.0852, inside the first rung. Send a market buy for 10 lots and you clear the 3 at 1.0852 and 7 of the 8 at 1.0853, so your 10 lots average out around 1.0853 — a fraction worse than the top quote. The 20 lots sitting at 1.0854 is a modest wall: a small buyer will not shift it, and price may hesitate there until it fills or lifts.
Why it matters
For anyone trading real size, the DOM is where slippage is decided. It shows whether the market can take your order without moving, or whether you will walk the price up as you fill. It also reveals liquidity that a single quote hides — a tight spread with almost nothing behind it is thinner than it looks. For most retail forex traders on small size, the DOM matters less, because your order is smaller than the top rung and fills without touching the rest.
Common misconceptions
- Forex has no single order book. It is a decentralised market, so the DOM you see comes from your broker's own feed or its liquidity providers — a slice of the whole, not the entire market. Two brokers can show different depth.
- You only get a real DOM on ECN or raw-spread accounts. A market-maker or B-book broker sets your price internally and may show no depth at all, or a simulated one. cTrader and MT5 expose it; classic MT4 largely does not.
- Resting size can be a bluff. Large orders are sometimes placed to influence others and pulled before they fill, so the wall you see is not a promise it will hold.
The takeaway: the DOM turns one price into a picture of the size behind it. On an ECN account it tells you what your order will really cost to fill; on a market-maker account, treat any depth shown with suspicion.
The Karnek note
Karnek reads your live terminal to show the fills your account actually got — the prices, the sizes, the slippage against where you aimed — which is the DOM's effect made real after the trade. It monitors read-only and can never place or pull an order in the book. If a strategy trades more size than the depth can take, that slippage shows up in the numbers we read straight from the terminal.
Written and reviewed by the Karnek Research team. Last updated August 2026.
Educational content only - not financial advice. Past performance does not predict future results. Trading carries significant risk.