Rivers & gauges
What Is CFS? Cubic Feet per Second Explained
By the Water Level Atlas team · Last reviewed Oct 21, 2026
CFS stands for cubic feet per second. It is the standard US unit for river flow: the volume of water, in cubic feet, that passes a point in the river every second. One cfs is about 7.48 gallons per second, or 0.0283 cubic meters per second (m³/s).
What does one cubic foot per second look like?
A cubic foot is a box 1 ft (about 30 cm) on each side. USGS describes one cfs as that box of water moving past a point every second, which is about 7.5 gallons each second.
So if a river is flowing at 1,000 cfs, imagine one thousand of those boxes of water passing the gauge every second, all day and night.
How do I convert cfs?
These conversions use USGS definitions. Numbers are rounded.
| Flow | Equals |
|---|---|
| 1 cfs | 7.48 gallons per second |
| 1 cfs | 448.8 gallons per minute |
| 1 cfs | 0.0283 m³/s (28.3 liters per second) |
| 1 m³/s | about 35.3 cfs |
| 1 cfs flowing for one day | 86,400 cubic feet, about 1.98 acre-feet, about 646,000 gallons |
An acre-foot is the amount of water that would cover one acre to a depth of one foot: 43,560 cubic feet, or about 326,000 gallons. Reservoir storage is often given in acre-feet, which is why the "1 cfs for a day = about 2 acre-feet" rule is handy. See reservoir storage and percent full.
Worked example (round numbers, not a real river)
Say a gauge reads 1,000 cfs.
- In metric: 1,000 × 0.0283 = about 28 m³/s.
- In gallons: 1,000 × 7.48 = about 7,500 gallons every second.
- Over one day: 1,000 × 1.98 = about 1,980 acre-feet, or roughly 646 million gallons.
How is cfs measured?
It is not measured directly by a sensor. USGS gauges record the height of the water every 15 minutes. Field crews regularly measure the flow by hand, working out the river's cross-section area and the water's speed, and multiplying them. Those hand measurements build a rating curve that turns each height reading into a flow in cfs. See how river gauges work and gauge height vs streamflow.
Is cfs the same as how high the river is?
No. Flow (cfs) and gauge height (feet) are different things. The link between them is different at every gauge, because it depends on the shape, size, slope and roughness of the channel at that spot. Flow tells you how much water is moving. Gauge height tells you how high the surface is above a local reference point.
Why do flows vary so much between rivers?
A small creek and a large river are not on the same scale, so their flow numbers can be very far apart. The main reasons:
- How much land drains to the gauge. A gauge far down a big river collects water from a much larger area than one on a headwater stream.
- Rain and snow. Observed and forecast rain and snow, and the amount of snow waiting to melt, drive how much water reaches the river. NOAA river forecasters model all of these.
- Soil and land. How wet the soil already is, and the basin's shape, slope, land cover and vegetation, affect how much rain runs off and how fast.
- Dams and diversions. Releases from reservoirs run by agencies such as the US Army Corps of Engineers and the Bureau of Reclamation can raise or cut flow below a dam. See who manages US reservoirs.
Flow at a single gauge also varies a lot through the year. That is why a raw number means little on its own. A flow that is high for a small creek may be very low for a big river. The useful question is: how does today's flow compare with what is normal at this gauge, on this date?
Using this on Water Level Atlas
Our river pages show the latest flow in cfs at the top, next to gauge height in feet, and compare it with the normal range for the date from USGS statistics for that gauge. That comparison is usually more useful than the raw number. See normal for the date for how that range works, and our methodology page for data sources.