Polymarket Liquidity, Explained

• Depth — contracts resting at each price level; top-of-book depth is the first two rows (bid and ask).
• Spread — the gap between the best bid and best ask, in ticks (0.01 per level).
• Volume — executed contracts over time; it measures past flow, not present depth.
• Mid — the halfway point between best bid and ask; not necessarily an executable price.

Across 298 resolved BTC five-minute contracts and 17,880 one-second snapshots, the winning side rested at 0.99 or better 98.6% of the time, with a median top-of-book size of 42,254 shares. A 42,000-share bid at 0.99 in the final minute looks like deep liquidity; it is actually the answer to the market, and there is nothing to buy against it.

In an ETH inversion measured this site, resting bid depth fell 96% in one minute while ask depth rose almost sixfold before the price followed. Depth does not dry up first — it inverts, and the price catches up.

Liquidity you can use is size on your side of the book at a price you accept. Liquidity you cannot use is size resting where the market has already made up its mind — the 0.99 bid with no ask in a market about to resolve.

That is the distinction a top-of-book price feed cannot give you. A full book shows whether the apparent size is real counterparty or the reflection of a settled outcome.

• For a liquid and an illiquid market, pull the top-of-book sizes at 250ms for one day and print the per-frame bid/ask size medians; the ratio of the two medians is your first liquidity number.
• Count the frames with resting size on both sides (two-sided share); the measured Up/Down books are one-sided most of the time, and the share is the honest liquidity measure.
• Correlate the one-sided share with the median trade size (42,254 shares in the measured sample); the comparison shows what "liquidity" actually means when the book is thin.
• Repeat across sports and Up/Down, and record the two-sided share per series; the contrast is the page's argument in one table.

Liquidity on Polymarket is not a depth number but a side number: the venue's books are one-sided at least 90% of the time on the measured families, so the practical question is not "how deep" but "which side, and can I cross it."

The depth redistribution during repricings — ETH bid −96%, ask +491% on the August 23 window — shows liquidity as a flow between sides: the bid vacuum and ask pileup are the same event measured from two sides.

Liquidity is the most venue-specific concept on this site; the one-sided share is the metric that describes it, and the archive makes it per-market.

Never quote a market as "liquid" from a mid chart; quote the two-sided share and the top-of-book sizes, both measured.

Use the measured medians (42,254 / 65,081) as the yardstick for what size crosses these books; liquidity claims above that band need the frames to support them.

Liquidity is the keystone of the catalog: later concepts measure variants of it, and the measured one-side share is the number the illiquid page cites.

Read it with the order-book and depth explainers to get the full view: the ladder explains the levels, this page explains the sides, and depth explains the sizes.

When buying or selling on the venue, the page's rule applies before any fill: check both sides first.

Liquidity on this venue is a sides-and-sizes statement, and the one-sided share plus top-of-book depths are its honest numbers.

Benchmark every "liquid" claim against the measured texture before accepting it; the archive makes the benchmark a query.

Use the median trade (42,254) as the size unit that actually moves these books.

• Order book data
• Price history
• Crypto data
• Provider matrix