Trade size refers to the quantity or volume of securities, commodities, or financial instruments involved in a single transaction. Trade size affects market impact, execution costs, and liquidity requirements. Larger trade sizes may require special handling, block trading networks, or algorithmic execution to minimize market disruption.

Trade size considerations include available liquidity, position sizing rules, and market impact analysis. Institutional traders often break large orders into smaller sizes to optimize execution, while retail traders typically deal with standard lot sizes. Understanding trade size effects helps optimize execution strategies and cost management.

Real-world example: An institutional investor wanting to buy 1 million shares of Apple breaks the order into 100 smaller trades of 10,000 shares each throughout the day to minimize market impact and achieve better average execution prices.