Cubic Meters per Second to CFS Converter

This calculator converts a flow rate given in cubic meters per second (m³/s) to cubic feet per second (cfs or ft³/s). You enter the flow rate in m³/s, and the calculator returns the equivalent in cfs, along with the flow in liters per second and gallons per minute for context. The conversion uses the exact relationship: 1 cubic meter equals 35.314666721489 cubic feet.

Formula

The conversion is a straightforward unit multiplication:

Q_cfs = Q_m³/s × 35.314666721489

• Q_m³/s – flow rate in cubic meters per second (m³/s)
• Q_cfs – flow rate in cubic feet per second (ft³/s, commonly written cfs)
• 35.314666721489 – exact number of cubic feet in one cubic meter (1 m = 3.28083989501312 ft, so 1 m³ = 3.28083989501312³ ft³)

For quick mental estimates, use 35.3 as the multiplier. The exact value matters only when you need precision beyond about four significant figures.

Worked Example

Using the default value of 1 m³/s from the calculator:

1. Start with the flow: 1 m³/s
2. Multiply by the conversion factor: 1 × 35.314666721489 = 35.314666721489 ft³/s
3. Round to three decimal places: 35.315 cfs

The calculator shows 35.315 cfs, matching the result above. For a more typical river flow of 100 m³/s, the result would be 3,531.467 cfs.

When to Use This Conversion

Flow rate units appear in hydrology, civil engineering, water treatment, and environmental reporting. In the United States, streamflow data from the USGS is often reported in cfs, while most other countries use m³/s. If you are comparing international data, designing a pipeline, or reading a flood report, you will likely need to switch between these units.

The conversion is also common in:

• River and stream discharge measurements
• Water supply and irrigation system design
• Wastewater treatment plant capacity calculations
• Hydroelectric power generation assessments
• Environmental impact studies

How to Read the Result

The output in cfs tells you the volume of water passing a point each second. For example, 35.315 cfs means 35.315 cubic feet of water flows by every second. To put that in perspective, a typical garden hose flows about 0.02 cfs, while a large river like the Mississippi at New Orleans averages around 600,000 cfs. The calculator also shows liters per second (L/s) and gallons per minute (GPM) to help you relate to everyday quantities.

Common Mistakes and Unit Mix-ups

The most frequent error is using the wrong conversion factor. Some sources round to 35.31, which is fine for most purposes, but using 35.3 introduces a 0.04% error. Another common mistake is confusing cubic feet per second with cubic feet per minute (cfm) or gallons per minute (gpm). Remember:

• 1 m³/s = 35.3147 cfs
• 1 m³/s = 2,118.88 cfm (multiply cfs by 60)
• 1 m³/s = 15,850.3 gpm (multiply cfs by 448.831)

Also, be careful with the difference between US gallons and imperial gallons. The calculator uses US gallons (231 cubic inches). If you need imperial gallons, multiply the US value by 0.832674.

Limitations of the Formula

This conversion is purely dimensional – it changes units without altering the physical meaning of the flow rate. It works for any fluid, whether water, oil, or air. However, it does not account for temperature, pressure, or density. If you need mass flow rate (kg/s) rather than volumetric flow rate, you must multiply by the fluid’s density. Also, for gases, volumetric flow is often stated at standard conditions (e.g., 20°C and 1 atm); the conversion factor remains the same, but the actual volume changes with temperature and pressure.

Frequently Asked Questions

How many cfs is 1 m³/s?

Exactly 35.314666721489 cubic feet per second. For everyday use, 35.3 cfs is a close approximation. So if a river is flowing at 2 m³/s, that is about 70.6 cfs.

Why do Americans use cfs instead of m³/s?

The United States historically uses the imperial/customary system for many engineering applications. Streamflow data in the US has been reported in cfs for over a century, particularly by the US Geological Survey. Most other countries adopted the metric system and use m³/s. Both units measure the same physical quantity – volume per time.

How do I convert cfs back to m³/s?

Divide the cfs value by 35.314666721489. For example, 100 cfs ÷ 35.3147 ≈ 2.832 m³/s. The calculator above can be used in reverse by entering the cfs value and dividing, but it is easier to just divide manually.

What is the difference between cfs and gpm?

Cubic feet per second (cfs) and gallons per minute (gpm) both measure flow rate but use different units and time bases. 1 cfs = 448.831 gallons per minute. GPM is common for smaller flows like pumps and household plumbing, while cfs is used for rivers and large pipelines.

Is cfs the same as cubic meters per second?

No, they are different units for the same quantity. 1 m³/s is about 35.315 cfs. The numerical value changes depending on the unit, but the actual flow rate is identical. Think of it like converting between miles and kilometers – the distance is the same, just expressed differently.

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in m3s | Flow rate | m³/s | 1 | 0
out cfs | Flow rate | ft³/s | m3s * 35.314666721489 | 3
out lps | Flow rate | L/s | m3s * 1000 | 1
out gpm | Flow rate | gal/min | m3s * 15850.323141489 | 1