What is market liquidity?

The definition, and its awkward property

Liquidity is the ability to convert an asset to cash, or cash to the asset, quickly, in size, near the current price.

Notice what that describes: what would happen if you traded. It is a counterfactual about an action not taken, and counterfactuals do not appear in data feeds. Every liquidity measure in existence is therefore a proxy — an observable quantity believed to correlate with the thing you actually care about.

That is not a reason to ignore liquidity measures. It is a reason to know which proxy you are looking at and how it fails.

Four dimensions

A single "liquidity score" collapses four distinct properties into one number. An asset can be tight and shallow — narrow spread, but the book empties after a modest order. Another can be wide and deep. They are not interchangeable, and one figure cannot express the difference.

Turnover: the practical proxy

The most useful liquidity measure available from public crypto data is turnover — 24-hour volume divided by market capitalisation.

Its advantages are real:

• Available for every tracked asset, with no venue-level data required.
• Comparable across sizes, because dividing by market cap removes the scale effect.
• Unambiguous at the low end: an asset turning over 0.1 % per day genuinely cannot absorb a large position quickly.

Where turnover stops working

It measures completed trades, not available depth. Two assets with identical turnover can have entirely different order books — one absorbing steady flow, the other seeing the same volume arrive as a handful of trades that each moved the price several percent.

The second case is worse and looks identical. High turnover on a thin book means price is moving on modest flow, which is closer to a warning than a reassurance.

Reported volume is also unverified. Wash trading inflates the numerator, and it is most common exactly where turnover attracts the most attention: small assets on small venues. Moonboard applies no wash-trading filter, and LMR cannot distinguish genuine turnover from manufactured turnover.

Price impact is non-linear

A practical point that a single liquidity number cannot convey: doubling an order size can more than double its price impact, because the order consumes progressively worse levels of a book that thins with distance from the mid.

This is why a turnover ranking cannot be converted into an executable size, and why the gap between the two widens for exactly the small, thin assets where high turnover rankings look most interesting.

Why liquidity matters beyond execution

• Price reliability. A price from a thin market represents the last small trade, not a level at which meaningful size could transact.
• Volatility. Illiquid assets move more per unit of flow, which shows up as higher volatility.
• Manipulation cost. Moving a thin market is cheap. Liquidity is, among other things, a measure of how expensive manipulation would be.
• Exit risk. Liquidity tends to disappear precisely when it is most needed — during stress, when everyone wants the same side.