Polymarket Tick Size, Explained

• The official book payload carries a tick_size of 0.01 per token and a min_order_size of 1 share.
• Every bid and ask sits on the 0.01 grid; a one-tick spread means a 0.99 bid meeting a 1.00 ask or a 0.50–0.51 market.
• The mid can land off-grid (0.4995) when the book is asymmetric — a sub-tick number that does not exist as a tradeable price.
• Neg-risk markets can appear with related token sets where prices reflect opposite sides (Yes at 0.01 equals No at 0.99).

A fixed tick makes the spread shock-absorbing: at 0.99 the winning side can tighten to a single tick while the losing side drains. Measured BTC settlement books held 0.990 for entire final minutes, with size growing from ~4,600 to 67,000+ shares on that fixed grid.

The flip side is the empty-book hazard: with a 0.01 grid, a missing level can create a 99.6-cent chasm around the mid, printing a probability nobody can buy. Ticks constrain what is quoted, not what is actually there.

Research that needs sub-tick insight has to watch two things the grid hides: the depth at each tick, and the sub-tick mid (0.4995) that signals imbalance. Recorded 250ms books preserve both at the same timestamp.

Using recorded rows, spread = (ask - bid) in ticks, imbalance = bidDepth vs askDepth at the top level, and every quote is pinned to the 0.01 grid — so tick-based strategies replay exactly.

• Identify the tick sizes in a ladder frame: 0.5-cent steps on the tighter grids and 1-cent steps deeper; record the step where the market is quoting.
• Compute how many ticks the executable floor sits above/below the mid in a one-sided frame; the tick distance is the real price of immediacy.
• Measure the tick frequency across the day: the share of frames exactly on-grid (98.6% of the measured sample at 0.99/0.995 sits within two ticks of the boundary) — tick discipline is the venue's default.
• Find the frames where the ladder stepped multiple ticks in one second; the 99.6-cent one-second pass is the maximum documented tick excursion.

Tick size is the smallest price increment on the ladder, and on Polymarket it structures everything: the round grid, the tight two-sided gaps, and the coarse jumps when a live market reprices.

The venue's tick discipline is a measured fact — quotes hug the 0.5-cent/1-cent steps so tightly that 98.6% of sampled frames price within two cents of the settlement boundary — and the archive lets any page verify it.

Verify tick discipline on your own pull: count the frames whose executable price sits exactly on the 0.5-cent or 1-cent grid across a day; the measured 98.6% share is the baseline your day should approach, and a market that drifts off-grid is a market worth re-reading.

Tick size is the venue's granularity: 0.5-cent steps on tight grids, 1-cent deeper, and the ladder moves in those units only.

Tick distance, not mid distance, is the honest price of immediacy on a one-sided book.

The measured on-grid discipline (98.6% at 0.99/0.995) is the empirical signature of the tick structure; the archive makes it reproducible.

Tick size is the venue's granularity constant, cited by every ladder discussion and the price-level page.

Read it with the spread and price-bounds explainers to see the tick as the unit of both quotes and gaps.

The on-grid discipline measurement (98.6% at 0.99/0.995) is the empirical proof this page adds to the catalog.

Tick size sets the venue's granularity: 0.5-cent steps on tight grids, 1-cent deeper, and ladder moves in those units only.

The on-grid discipline is measured, not assumed; verify it on any market you study.

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