Trading Volume
The quantity of a stock bought and sold over a period — a measure of how much trading actually joined a price change.
In plain terms
Even the same 1% rise carries a different weight of meaning whether only a few traded it up or a great many crowded in. Volume shows "how much trading actually joined that price change."
One point to note: volume itself has no direction. For every buyer there was a seller. So what volume tells you is not "will it rise or fall" but "how much interest and conviction the move carried."
What it tells you
Volume is an easier signal to trust than price. Price can be nudged up or down briefly on small quantity, but volume shows exactly how much trading actually happened. So a price that only rises on thin volume may be a weak flow made by a few trades.
When volume suddenly jumps far above usual, it signals an attention-grabbing event like an earnings release or big news. But the mere fact that volume rose cannot be called "good interest" — volume alone cannot tell you who bought and who sold that quantity.
Formula
volume = the number of shares executed in the period (e.g. a day) dollar volume = volume × trading price (since the buy and sell sides are always equal in quantity, volume itself does not indicate the up/down direction)
What high or low means
When volume rises along with price, the rise is seen as carrying momentum. Conversely, if price rises while volume falls (especially at new highs), it means fewer people are joining, sometimes read as the rise weakening. Price and volume pointing in different directions like this is called "volume divergence."
⚠ There is a counterintuitive case too. A sudden surge in volume near a top looks like a good sign, but it may actually be latecomers buying the quantity a large investor unloaded — that is, ownership of the stock changing hands. "A lot of trading" does not mean "a lot of buyers."
Volume is not good when high and bad when low. It is a supplementary indicator of "how much conviction a price change carried," not which way price will go.
On earnings days, options expiration, and index-inclusion days, volume spikes temporarily. So do not look only at one day's figure — compare it with the usual average.
A small-cap with thin volume swings hard even on little trading and is hard to buy and sell at your price (this is called "lacking liquidity"). Volume is also unrelated to a company's value, and is not itself a buy/sell signal.
During the 2021 GameStop (GME) episode, volume exploded and the price rose sharply in a short span. But much of that volume came not from company results but from crowd psychology and a short squeeze, and when the heat faded the price fell fast.
It is a case showing that the simple idea "if volume surges, good interest has gathered" is not always right. Volume tells you how hot the market is, but not why it is hot.
Metrics to read alongside
See it in real stocks
Search US stocks on Stocklore to see Trading and other financial metrics alongside the sector average.
This explanation is for information and reference only and is not a recommendation to buy or sell any security. Investment decisions and their consequences are your own.