Short Volume
The share of a day's reported trading volume that broker-dealers marked as short sales and reported to FINRA — a daily activity number, not a count of shares currently sold short.
What it is
Short volume is the number of shares sold in trades that the executing broker-dealer marked as short sales during a single trading day, aggregated and published by FINRA from the trades reported to its facilities. It is usually expressed as a percentage: short volume divided by total reported volume for that day. It is a flow measure — it counts trades that happened on one day. That makes it different from short interest, which is a stock measure: the number of shares still sold short and not yet covered as of a settlement date. Under SEC Regulation SHO, a short sale is any sale of a security the seller does not own, or any sale consummated by delivering a security borrowed by or for the account of the seller; the order-marking rules require the seller's broker to mark each sale long, short, or short exempt, and it is those marks that the daily file counts.
Why it matters
Short volume arrives daily, while short interest is published on a lag and only twice a month, so short volume is among the fastest publicly available windows into short-side activity. It can help you see whether short-side trading in a name is unusually heavy relative to its own recent history, and it is one input among many when trying to understand who is trading a stock. A pitfall is that a large share of reported short volume comes from market makers and other liquidity providers, who must mark a sale short whenever they fill a customer's buy order from flat or negative inventory, rather than from directional bearish positioning — so a high reading does not mean traders are betting against the company. A second limitation is that FINRA's file covers only trades reported through its own facilities, which is off-exchange volume rather than the whole consolidated tape, and same-day covering means many of the shorts counted here are already closed by the bell. Treat the number as a research signal about activity, never as a verdict on a company.
How it's calculated
FINRA publishes a daily file listing, per symbol, the short volume, the short exempt volume, and the total volume reported through its facilities — the trade reporting facilities, the ADF, and the ORF, which carry off-exchange trades rather than the full consolidated tape. The percentage is short volume divided by total reported volume for that same day, multiplied by 100, so it describes the short share of reported volume and not of all volume traded. Quintarthai reads the daily FINRA file and exposes that percentage as a screener filter, so you can set a floor or a ceiling on it. Because it is a per-day figure it is noisy on any single day, and it is normally read against the same stock's own recent range rather than against an absolute cutoff. No fixed threshold separates a high reading from a low one — that judgement depends on the name.
How Quintarthai uses it
In the Quintarthai stock screener (/app/), the Short Volume filter screens on the daily FINRA short volume percentage, one of the 231 available filters alongside the Liquidity category's Corwin-Schultz estimated bid-ask spread. It is shown for education and research with its methodology and caveats attached, never as advice.