What is CFS? Understanding River Flow Rates

If you've ever looked up river conditions before a kayaking, rafting, or fishing trip, you've almost certainly seen the acronym CFS. It's the most common metric used by the USGS (United States Geological Survey) to report streamflow, but what exactly does it mean?

The Definition of CFS

CFS stands for Cubic Feet per Second. It is a measure of the volume of water passing a specific point in a river during one second.

To visualize this, imagine a box that is one foot wide, one foot long, and one foot deep. That box holds exactly one cubic foot of water (which is about 7.48 gallons). If a river is flowing at 100 CFS, it means that 100 of those boxes are rolling past you every single second.

• 1 CFS = ~7.48 gallons per second
• 1,000 CFS = ~7,480 gallons per second

CFS vs. Gauge Height (Stage)

You will often see rivers measured in two ways: CFS (Discharge) and Feet (Gauge Height or Stage).

• Discharge (CFS): Measures the volume of water moving down the river.
• Gauge Height (Ft): Measures the depth of the water at the specific location where the physical gauge is mounted.

While both numbers rise and fall together, CFS is generally a much better indicator of how powerful a river will feel. A river that is 4 feet deep but 200 feet wide has vastly more water (and power) moving through it than a river that is 4 feet deep but only 20 feet wide.

Safety Tip: Always check both numbers! If a river's CFS is normal but the gauge height is unusually high, it could indicate a downstream blockage (like an ice jam or fallen trees) causing water to back up.

What is a "Good" CFS?

There is no universal "good" CFS because every river is uniquely shaped.

A flow of 500 CFS on a steep, narrow mountain creek might create raging, dangerous Class V whitewater. However, that exact same 500 CFS on the massive, wide Mississippi River would look like a dry puddle.

Because of this, you have to know the specific river's thresholds.

At ClearGauge, we do the heavy lifting for you. We calculate the historical percentiles for every single gauge to determine if the river is running Low, Normal, High, or Flood relative to its own unique history.

How Does the USGS Measure CFS?

Most modern USGS streamgages don't actually measure CFS directly. Instead, they measure the gauge height (using floats, pressure sensors, or radar).

The USGS sends hydrologists out to the river periodically to physically measure the width, depth, and velocity of the water at various gauge heights. They use this data to create a mathematical formula called a Rating Curve. The rating curve translates the simple depth measurement (feet) into the complex volume calculation (CFS) automatically!

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Ready to hit the water? Now that you know how to read the flow, check out the live conditions on your local rivers to see what the CFS is looking like today!