Cubic feet per second (ft³/s) to Gallons per second (gal/s) conversion

Understanding Cubic feet per second to Gallons per second Conversion

Cubic feet per second ($ft^3/s$) and gallons per second ($gal/s$) are both units of volume flow rate, which describes how much volume moves past a point in a given amount of time. Cubic feet per second is common in hydrology, civil engineering, and large-scale water movement, while gallons per second is often easier to visualize for pumping systems, water supply, and industrial flow measurements.

Converting from $ft^3/s$ to $gal/s$ helps express the same flow in a unit that may be more familiar or better suited to a specific application. This is especially useful when comparing river discharge data, pump capacities, or treatment system flow rates.

Conversion Formula

To convert cubic feet per second to gallons per second, use the verified relationship:

$$1\ ft^3/s = 7.480515625\ gal/s$$

So the conversion formula is:

$$gal/s = ft^3/s \times 7.480515625$$

For reference, the inverse relationship is:

$$1\ gal/s = 0.1336806244556\ ft^3/s$$

Step-by-Step Example

Convert $12.5\ ft^3/s$ to gallons per second.

1. Write the formula

$$gal/s = ft^3/s \times 7.480515625$$

2. Substitute the value

$$gal/s = 12.5 \times 7.480515625$$

3. Calculate

$$gal/s = 93.5064453125$$

So:

$$12.5\ ft^3/s = 93.5064453125\ gal/s$$

Real-World Examples

• A small stream gauge may record a discharge of $3.2\ ft^3/s$, which equals $23.93765\ gal/s$.
• A stormwater outfall carrying $18\ ft^3/s$ corresponds to $134.64928125\ gal/s$.
• A municipal water transfer line operating at $40\ ft^3/s$ delivers $299.220625\ gal/s$.
• An industrial cooling-water system flowing at $0.75\ ft^3/s$ moves $5.61038671875\ gal/s$.

Interesting Facts

• Cubic feet per second, often abbreviated as cfs or ft³/s, is a standard unit used in the United States for reporting river discharge and open-channel flow. It is commonly seen in hydrologic data published by the U.S. Geological Survey. Source: USGS Water Science School
• The U.S. gallon used in this conversion is different from the imperial gallon used in some other countries, so gallon-based flow rates depend on which gallon definition is intended. Source: Wikipedia: Gallon

How to Convert Cubic feet per second to Gallons per second

To convert Cubic feet per second ($\text{ft}^3/\text{s}$) to Gallons per second ($\text{gal}/\text{s}$), multiply the flow rate by the conversion factor between cubic feet and gallons. For this conversion, $1\ \text{ft}^3/\text{s} = 7.480515625\ \text{gal}/\text{s}$.

1. Write the conversion factor:
   Use the known relationship:

   $$1\ \text{ft}^3/\text{s} = 7.480515625\ \text{gal}/\text{s}$$

2. Set up the multiplication:
   Multiply the given value, $25\ \text{ft}^3/\text{s}$, by the conversion factor:

   $$25\ \text{ft}^3/\text{s} \times 7.480515625\ \frac{\text{gal}/\text{s}}{\text{ft}^3/\text{s}}$$

3. Cancel the original unit:
   The $\text{ft}^3/\text{s}$ units cancel, leaving Gallons per second:

   $$25 \times 7.480515625 = 187.012890625$$

4. Result:

   $$25\ \text{ft}^3/\text{s} = 187.012890625\ \text{gal}/\text{s}$$

A quick way to check your work is to estimate $25 \times 7.5 \approx 187.5$, which is very close to the exact answer. Always make sure the original units cancel so the final unit is $\text{gal}/\text{s}$.

What is the formula to convert Cubic feet per second to Gallons per second?

To convert Cubic feet per second to Gallons per second, multiply the flow rate by the verified factor $7.480515625$.
The formula is: $\text{gal/s} = \text{ft}^3/\text{s} \times 7.480515625$.

How many Gallons per second are in 1 Cubic foot per second?

There are exactly $7.480515625$ Gallons per second in $1$ Cubic foot per second.
This means $1\ \text{ft}^3/\text{s} = 7.480515625\ \text{gal/s}$.

Why would I convert ft3/s to gal/s?

This conversion is useful when comparing water flow rates in different measurement systems.
It is commonly used in plumbing, irrigation, water treatment, and pump sizing where gallon-based units are easier to interpret.

Can I use this conversion for water flow and other liquids?

Yes, this is a volume flow conversion, so it applies to any liquid or gas as long as the original flow rate is measured in $\text{ft}^3/\text{s}$.
The factor $7.480515625$ converts the volume unit from cubic feet to gallons within the same per-second time basis.

How do I convert a larger flow rate from ft3/s to gal/s?

Multiply the number of Cubic feet per second by $7.480515625$.
For example, if a flow is $5\ \text{ft}^3/\text{s}$, then the result is $5 \times 7.480515625\ \text{gal/s}$.

Is the conversion factor always the same?

Yes, the factor remains constant because $1\ \text{ft}^3$ is always equal to $7.480515625$ gallons.
As long as the time unit stays in seconds, the conversion from $\text{ft}^3/\text{s}$ to $\text{gal/s}$ does not change.