What it is

Raw volume is hard to act on because it varies wildly across symbols and across the trading day. Relative volume (RVOL) fixes this by comparing current volume to a baseline of what is normal for that same symbol. The result is a ratio: an RVOL of 1.0 means today's pace is average, 2.0 means twice the usual activity, and 0.5 means half. Suddenly a meaningless raw number becomes an interpretable signal of unusual participation.

A volume spike is a single period whose volume jumps far above its recent neighbours - the histogram bar that towers over the rest. Spikes mark moments when something changed: news hit, a level broke, or large players stepped in.

How it works

The baseline is usually a simple average of recent volume - for example, the 20-day average daily volume, or for intraday work, the average volume seen at this same time of day over the past N days. The time-of-day adjustment matters: the first and last 30 minutes are naturally heavy, so comparing 09:45 volume to a flat daily average would flag a spike that is really just the normal open.

The formula is simply:

• RVOL = current period volume / average volume for the comparable period

A spike is then any bar whose RVOL crosses a threshold you set - commonly 2x or 3x the average. The higher the threshold, the rarer and more meaningful the events it catches.

How to use it

Relative volume is most powerful as a filter and a context tag, not a standalone buy or sell trigger.

• As a filter: before acting on any price signal, check RVOL. A breakout at RVOL 0.6 is happening on apathy and is more likely to fail; the same breakout at RVOL 2.5 has crowd participation behind it.
• As an alert: scanning a watchlist for symbols where RVOL suddenly exceeds 3x surfaces names that something is happening to right now, before you have read any news.
• As context: a spike at a key support or resistance level tells you that level is being heavily contested - a high-information moment.

A worked example

Suppose a stock normally trades about 10 million shares a day. You are watching it approach resistance.

1. By 11:00, it has already traded 9 million shares. Its average volume by 11:00 is usually 4 million, so RVOL is 9 / 4 = 2.25.
2. Price pushes through resistance on the next bar, and that single bar prints 3x its normal volume.
3. The elevated RVOL plus the spike at the breakout point tells you participation is genuinely heavy - the breakout has backing.
4. Contrast with a day where price drifts above resistance on RVOL 0.5: the same price action, but no one is participating, so you treat it with suspicion and demand further confirmation.

Key takeaway: Relative volume normalises activity against a symbol's own typical pace, turning raw volume into a comparable ratio. Use spikes and high RVOL as a filter and context tag - they validate price signals rather than generate them.

Strengths & limits

RVOL is portable: a value of 2.0 means the same thing on a megacap and a small company, which raw volume can never offer. It is excellent for ranking and scanning many symbols at once.

Be aware of the traps. Scheduled events - earnings, index rebalancing, options expiry - produce predictable spikes that say nothing about a directional edge; check the calendar before reacting. Early in the session, intraday RVOL is computed from very little data and can be jumpy. And a spike confirms that participation surged, not which direction the crowd was right about - always read it together with price, never alone.