What it is

Volume is the number of shares (or contracts) that change hands over a chosen period. On a daily chart, each bar's volume counts every share traded that day; on a five-minute chart, it counts the trades inside each five-minute window. Every transaction has a buyer and a seller, so volume does not tell you whether "buyers" or "sellers" won - it tells you how much business got done.

Think of price as what happened and volume as how many people cared. A 3% gain on a quiet day and a 3% gain on a frantic day look identical on a price chart, but they mean very different things. Volume is the participation behind the print.

How it works

Volume is usually drawn as a histogram beneath the price chart, one bar per period. Many platforms colour each volume bar green when the period closed up and red when it closed down - a rough hint of which side felt more urgent, though it is only a shortcut.

The single most useful idea is comparison. A raw number like 42 million shares means nothing on its own. You compare it to the same symbol's recent typical volume:

• Above-average volume signals strong interest and broad participation.
• Below-average volume signals apathy - few participants, thin conviction.

Volume also tends to cluster around events: earnings releases, news, the market open and close, and index rebalancing days. Knowing the calendar helps you avoid misreading a routine spike as a meaningful signal.

How to read it

Use volume to judge the quality of a price move rather than to predict direction by itself.

• Price up on rising volume - the advance has broad backing; the move has conviction.
• Price up on falling volume - the advance is running on fumes; fewer buyers each day is a warning that momentum may fade.
• Price down on rising volume - selling pressure is real and broad; the decline is being confirmed.
• A breakout on heavy volume is far more trustworthy than a breakout on thin volume, which often fails and reverses.

This is the principle of confirmation: a price move confirmed by volume carries more weight than the same move on quiet trade. When price and volume agree, you have a cleaner read; when they diverge, stay cautious.

Key takeaway: Volume measures participation, not direction. Use it to confirm price: a move backed by above-average volume has conviction, while a move on thin volume deserves scepticism.

Strengths & limits

Volume is one of the few inputs that is not derived from price - it adds genuinely new information, which is why it pairs so well with any price-based method. It is also simple and available for free on virtually every chart.

The limits matter too. Volume is noisy and event-driven, so a single big bar can mislead. It is not directly comparable across very different symbols - a megacap and a small company trade on completely different scales - which is exactly why you measure each symbol against its own history rather than an absolute threshold.