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What is a market order?
A market order is an instruction to buy or sell straight away at whatever price is available. It usually fills immediately, but the price it fills at is not fixed in advance.
What it means for you
The SEC notes the last-traded price is not necessarily the price a market order gets, and in fast markets parts of a large order can fill at different prices. In crypto, a big market order on a thin order book can sell well below the price on screen.
How it works
A market order takes whatever the other side of the book offers right now: a buy fills against the lowest asks, a sell against the highest bids. That is why it usually executes immediately but at an unknown price. The SEC notes the last-traded price shown on screen is not necessarily the fill price, and that other orders can be executed first. If the order is larger than the quantity at the top level, the remainder fills at worse levels, and in a fast-moving market parts of it can fill at different prices. A stop order turns into a market order when its trigger price is reached.
An example
Say you place a market order to buy 1,000 units when the lowest ask is 3 dollars. 500 units are offered at 3; the rest sit at 3.10. You pay 3,050 dollars, not 3,000.
Sources: SEC Investor Bulletin: Trading Basics, CFTC: Glossary · checked 4 October 2026
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