Why you should know this
The best bid and ask show only the front door of the market. Behind them sit more orders at different prices. If our size is larger than the quantity at the first level, execution walks through that depth.
This is where a simple quote becomes a practical trading decision. Reading the book helps us estimate slippage, choose order size, recognize thin markets and plan exits. It does not let us predict every cancellation or hidden order.
What an order book contains
A central limit order book records eligible resting buy and sell orders for one pair on one venue.
The bid side usually lists buyers, with the highest price closest to the middle. The ask side lists sellers, with the lowest price closest to the middle.
A simplified fictional Token A/PHP book might look like this:
| Asks | Quantity |
|---|---|
| ₱103 | 300 |
| ₱102 | 200 |
| ₱101 | 100 |
| Bids | Quantity |
|---|---|
| ₱100 | 150 |
| ₱99 | 250 |
| ₱98 | 500 |
The best ask is ₱101. The best bid is ₱100. The spread is ₱1.
Price level versus individual order
A row may combine several individual orders at the same price. The displayed 300 units at ₱103 could belong to one participant or many. The interface may also group nearby prices into a wider display bucket.
Do not infer identity or coordination from a row. We see eligible displayed interest according to that venue’s data presentation, not the complete motives behind it.
Cumulative depth
Cumulative depth adds quantities from the best price outward.
On the ask side above:
- up to ₱101: 100 units;
- up to ₱102: 300 units total;
- up to ₱103: 600 units total.
A market buy for 450 units could take:
- 100 at ₱101;
- 200 at ₱102;
- 150 at ₱103.
Its quote cost is:
(100 × 101) + (200 × 102) + (150 × 103) = ₱45,950
Average fill:
₱45,950 ÷ 450 = ₱102.11 approximately.
The best ask was ₱101, but only the first 100 units were offered there.
Walking the bid side
If a seller sends a market order for 600 units, it could consume:
- 150 at ₱100;
- 250 at ₱99;
- 200 at ₱98.
Proceeds before fees:
(150 × 100) + (250 × 99) + (200 × 98) = ₱59,350
Average fill:
₱59,350 ÷ 600 = ₱98.92 approximately.
The best bid of ₱100 did not apply to the full order.
Depth chart: useful summary, not prophecy
A depth chart turns cumulative bids and asks into two curves. It can quickly show where visible quantity is concentrated.
But the chart is a snapshot. Orders can be added, cancelled, filled or moved. A large “wall” may disappear before price reaches it. Other liquidity may appear only when the market moves.
Use depth to estimate current conditions, not to declare that price cannot cross a wall.
Price-time priority
Many continuous order books use price-time priority:
- Better price receives priority.
- At the same price, earlier eligible orders receive priority.
If two sell limits sit at ₱101, the one accepted first is normally ahead, subject to the venue’s specific rules. Cancelling and replacing may lose time priority.
This matters for passive traders: seeing trades at our limit price does not always mean our order should already be filled. Earlier quantity may still be ahead.
Displayed liquidity can vanish
Displayed orders are not deposits locked for our personal use. Until matched, eligible orders may often be cancelled or changed. During fast news, several levels can disappear before a market order arrives.
Therefore an average-fill estimate is a scenario, not a guarantee. The larger our size and the faster the market, the less confidence we should place in a static screenshot.
Hidden, reserve and off-book liquidity
Some markets may support hidden or reserve instructions, while brokers and OTC desks can hold liquidity outside the public book. Not every participant or available transaction appears in the visible rows.
The opposite is also true: visible size may not remain. Order-book reading is valuable precisely because it is incomplete but actionable information—not complete truth.
False walls and manipulation caution
Submitting orders with no genuine intent to execute can raise market-integrity concerns in regulated markets, and crypto venues may face similar abusive behavior. However, a cancelled wall alone does not prove manipulation. Legitimate participants cancel when risk, inventory or price changes.
Do not accuse a named trader or venue from a screenshot. Treat sudden cancellation as an execution-risk signal and preserve evidence for the platform or regulator if other suspicious facts exist.
One venue is not the whole market
Every venue has its own order book. A thin PHP book may coexist with deep global stablecoin markets. Prices can influence one another through participants, but quantities are not automatically shared.
Comparing a global volume number with local executable depth can be misleading. Our order fills where it is sent.
The DEPTH check
Before placing a meaningful order:
- D — Direction: buys consume asks; sells consume bids.
- E — Each level: how much quantity is available at each price?
- P — Price impact: what average and worst price does the static book imply?
- T — Time: how quickly is the book changing?
- H — Hidden uncertainty: cancellations, other venues and undisplayed liquidity?
If the implied worst price exceeds the plan, reduce size, use a controlled limit or decline the trade.
Philippine practical scenario
Miguel wants to convert crypto to PHP. The top bid appears attractive, but it covers only a small fraction of his amount. A larger sell would move down several levels.
He compares:
- smaller staged orders;
- a limit order with non-fill risk;
- another verified route;
- the total PHP after trading and Withdrawal costs;
- whether delaying is acceptable.
The order book helps with one stage. It does not verify the provider, bank route or final availability.
Common mistakes
- Looking only at the best bid or ask.
- Treating a wall as guaranteed support or resistance.
- Ignoring cumulative quantity.
- Forgetting that order rows may be aggregated.
- Assuming trades at our limit guarantee our place has reached the front.
- Using global volume to justify local order size.
- Accusing manipulation from cancellation alone.
A no-money depth lab
Copy the fictional book above. Calculate:
- Average fill for a 250-unit market buy.
- Average fill for a 400-unit market sell.
- Unfilled quantity if a 450-unit buy limit is capped at ₱102.
- Which side matters for a planned crypto-to-PHP sale.
- Three reasons the actual result could differ from the screenshot.
How this connects to market mastery
Order-book literacy turns liquidity from a vague word into quantities and prices. It prepares us to calculate maker/taker behavior, slippage, partial fills and execution quality.
Mastery does not mean predicting every order change. It means sizing the decision so that ordinary uncertainty does not break the plan.
Key takeaways and check
- Bids are buy interest; asks are sell interest.
- Cumulative depth shows how quantity builds away from the best price.
- Larger orders can fill across several levels.
- Price-time priority affects queue position.
- Displayed liquidity is useful but not guaranteed.
Market Explorer check: Walk a 450-unit market buy through the sample book and explain why ₱101 is not the average fill.
*Cryptocurrency and virtual asset transactions are highly volatile and irreversible, may result in significant losses, and do not guarantee returns; customers should trade only after understanding the risks involved.
