What it means
Every market needs a smallest step. Tick size is that step: the minimum amount by which a quoted price can move, and one of the quietest levers in market design.
US stocks trade in pennies today, but that is a choice, not a law of nature: for two centuries they traded in eighths and sixteenths of a dollar, and the 2001 move to decimals reshaped trading economics. The tick constrains competition: a one-cent grid means a market maker can step ahead of any quote for a penny, and narrower ticks intensify that penny-jumping while wider ticks protect displayed orders.
Regulators treat the tick as a dial: the SEC's Tick Size Pilot Program widened increments for small-cap stocks to test whether bigger steps would rebuild liquidity and research coverage in neglected names. The economics cut both ways: smaller ticks cut the spread investors pay to cross, but they also thin the reward for posting quotes, and market makers pull back when the queue pays less.
Different markets choose different grids: futures ticks vary by contract, bonds quote in fractions, and crypto exchanges pick increments so small the queue becomes a speed contest. The spread connection is direct: inactively traded stocks often have spreads pinned at one tick, so the tick is the spread, and changing it changes transaction costs immediately.
For a non-finance reader, tick size is the price tag gun's smallest digit: everything must be priced in whole ticks, and the size of the digit decides how finely sellers can undercut each other. Academic market-structure research treats the tick as one of the few policy variables that can be changed cleanly.
Studies of decimalization found spreads collapsed and depths fell, confirming the trade-off at national scale. Every later tick experiment is read against that benchmark.
In practice
Real-world examples.
Example
Halving a tick narrows the spread to one cent but cuts quoted depth by two-thirds.
Example
Retail fills improve while institutional impact costs quietly rise past the savings.
Example
The fix is a price-dependent grid: a ten-dollar stock and a ten-cent stock need different steps.
Formula
Calculation
No formula beyond the rule that all quotes must be multiples of the tick, so the minimum spread is one tick. The tick as a percentage of price, tick divided by share price, measures how coarse the grid is for that stock. Tick sizes are set by exchanges within regulator-approved frameworks and can be revised.
Worked example: with a one-cent tick, a $20.00 stock has a minimum spread of $0.01 / $20.00 = 0.05% of price, while a $2.00 stock has $0.01 / $2.00 = 0.5%, ten times coarser. An investor crossing a one-tick spread on 1,000 shares pays about 1,000 x $0.01 = $10 in spread cost, and a two-tick spread would cost $20. Halving the tick to half a cent would cut the one-tick cost on 1,000 shares from $10 to $5, though it might also thin the quoted depth.Case study
Seen in the real world.
This case study is fictional and illustrative. A made-up exchange product manager owns the tick schedule for a family of small-cap listings, and her inbox is a war between two lobbies. The market makers want finer ticks, the brokers who post displayed orders want wider ones, and both cite the same pilot data. Her experiment with one mid-cap name makes the trade-off physical: halving the tick narrows the spread from two cents to one, retail fills improve, and the quoted depth at best bid and offer falls by two-thirds as market makers stop paying to stand in line.
The stock's intraday volatility rises measurably, and the institutional desk that used to work orders patiently now pays more in impact than it saved in spread. Her memo to the listing committee distills the pilot literature into one sentence: the tick is a subsidy dial, and every tick regime chooses which side of the market gets subsidized. The committee's eventual compromise, a price-dependent tick grid that widens as share price falls, is the modern answer in miniature: a ten-dollar stock and a ten-cent stock should not share a grid. The two lobbies keep writing, but her dashboard settles the argument daily, one ticker at a time, in spread width against queue depth.
Her annual review of the grid includes a counterfactual exercise: replaying the year's trades under a wider tick to estimate what displayed liquidity would have looked like. The simulation never ends the debate, but it disciplines it. The two lobbies now argue about her model's assumptions instead of their slogans, which she counts as progress.
Watch out
Common mistakes.
- Assuming smaller is always better; finer ticks cut spreads but drain quoted liquidity and reward speed over patience.
- Forgetting the percentage lens; a one-cent tick is coarse for a penny stock and invisible for a thousand-dollar stock.
- Treating it as fixed; exchanges and regulators change tick regimes, and the 2001 decimalization and the tick pilot show the dial moves.
Questions
People also ask.
What is tick size?
The minimum price increment at which a security can be quoted, setting the grid for all bids, offers, and the minimum spread.
Why does it matter?
It shapes spreads, queue liquidity, and market-maker economics: narrower ticks cut spread costs but thin displayed depth.
Has it changed over time?
Yes: US stocks moved from fractions to pennies in 2001, and the SEC's tick pilot tested wider ticks for small caps.
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