Order book depth
How many contracts are available at each price level — the quantity you can actually fill, which is usually far less than the top quote suggests.
A quote of 45¢ might have 30 contracts behind it, then 200 at 47¢, then 1,000 at 52¢. Filling 500 contracts means walking through those levels at an average price well above 45¢. Prediction markets publish full books; sportsbooks do not, so ArbMonster reports sportsbook depth as unknown and caps sizing conservatively.
Every prediction-market card on ArbMonster is sized by walking the live book and averaging the fill, which is why the displayed profit is often smaller than a top-of-book calculation would suggest — and why it is achievable.
Measured on ArbMonster: Why top-of-book quotes mislead