Understanding Order Book Depth

The order book is the closest thing markets have to a live ledger of intent: every resting limit order, stacked by price, waiting to be filled. Read correctly, it tells you where liquidity actually sits. Read carelessly, it tells you a story that isn’t there.

Bids, asks, and the spread

The book has two sides. Bids are resting buy orders, sorted from the highest price down. Asks are resting sell orders, sorted from the lowest price up. The gap between the best bid and the best ask is the spread — the narrower it is, the more liquid the market is at that instant.

Depth is not static

Size at a price level isn’t a promise. Orders get pulled the moment the market moves toward them, which is why a wall of size sitting several levels away can vanish before price ever reaches it. Depth close to the current price is more informative than depth far from it, precisely because it’s harder to cancel without being filled first.

Reading depth without overreacting

• A large order near the touch can be genuine interest, or it can be designed to be seen and pulled (“spoofing” in its blunt form, though most large-size behavior is far more mundane than that). Treat it as a hypothesis, not a fact, until price actually interacts with it.
• Thinning depth on one side as price approaches a level is a better tell than the static size of the level itself — it suggests the resting orders are being worked or withdrawn, not held.
• Imbalance ratios (total bid size vs. total ask size within a fixed distance of the touch) are more stable signals than watching any single price level in isolation.

Where this fits in a workflow

Order book depth is a short-horizon tool — it tells you about liquidity in the next few ticks, not about tomorrow’s trend. Pair it with the timeframe you’re actually trading: for anything beyond a scalp, the book is context for your execution, not a reason to change your thesis.