Flow Rate Calculator
Calculate pipe flow rate from diameter and velocity, or volumetric flow from volume and time, in L/s, L/min and m³/h.
Flow rate
3.93 L/s
Litres per minute
235.62 L/min
Litres per hour
14,148 L/h
Cubic metres per second
0 m³/s
Pipe flow rate = cross-section area × velocity (Q = A × v).
Flow Rate Calculator on True Calculator gives you an instant, accurate answer with no sign-up and no app install. Calculate pipe flow rate from diameter and velocity, or volumetric flow from volume and time, in L/s, L/min and m³/h. Every result shows the formula and a worked example so you can verify the calculation yourself, and all values are computed in your own browser — your numbers never leave your device.
Popular uses: flow rate calculator · pipe flow calculator · water flow rate calculator
Reviewed by the True Calculator team · Last updated: August 2026
How We Calculate
This calculator uses standard physics and chemistry formulas verified by our team. All calculations are performed instantly in your browser using JavaScript — no data is sent to any server.
Formulas follow standard scientific definitions and physical constants, consistent with what is taught in school and university courses.
When to Use This Calculator
Flow rate decides the size of pumps, pipes and tanks across India — from a 1 HP monoblock filling an overhead tank to canal irrigation in Punjab and Tamil Nadu. Plumbers need it to check whether a borewell pump matches the building's daily demand, and factory engineers use it to design cooling water circuits. The volume-over-time mode needs no instruments: time how long it takes to fill a 200 litre drum and you know the pump's real output, which often differs from the nameplate. Whether you think in L/min, m³/h or L/s, this calculator converts between them and tells you whether the infrastructure can actually deliver.
How to Use This Calculator
- Step 1: Choose 'Pipe flow' for Q = A × v, or 'Volume / time' for a bucket-and-stopwatch measurement.
- Step 2: For pipe flow, enter the pipe diameter in mm and the water velocity in m/s.
- Step 3: For volume over time, enter the volume in litres and the time in seconds.
- Step 4: Read the flow in L/s, L/min and m³/s — pick the unit your pump or canal uses.
Worked Example
A 50 mm PVC pipe delivering water at 2 m/s has a cross-section of π × (0.025)² = 0.00196 m², so the flow rate is 0.00196 × 2 = 0.00393 m³/s — shown as 3.93 L/s or 235.62 L/min. That tells a farmer how long a half-acre irrigation channel takes to fill. Using the other mode, a builder who collects 500 litres from a pump in 60 seconds gets 8.33 L/s, which converts to exactly 30 m³/h — the number printed on pump nameplates.
Tips and Common Mistakes
- •Tip 1: Compare the result with the pump's rated L/min on its nameplate to check for a clogged or undersized line.
- •Tip 2: For canals and channels, use volume ÷ time with a known container rather than estimating pipe diameter.
- •Tip 3: Flow rate through a pipe rises with the square of the diameter — a 75 mm pipe carries 2.25× more than a 50 mm one at the same velocity.
- ✗Mistake 1: Mixing millimetres and metres — the diameter must be in mm and velocity in m/s.
- ✗Mistake 2: Measuring time in minutes and entering it as seconds; keep everything in seconds.
Frequently Asked Questions
How is pipe flow rate calculated?
Q = A × v, where A is the cross-section area of the pipe (π × r²) and v is the flow velocity. A 50 mm pipe at 2 m/s delivers about 3.93 L/s or 236 L/min.
What is the difference between L/s and L/min?
They are the same flow expressed in different time units. 1 L/s equals 60 L/min, since one minute has 60 seconds. The calculator shows both.
Can I measure flow from a bucket and a stopwatch?
Yes. Use the 'Volume / time' mode: fill a known-volume container, time how long it takes, and enter both. 500 litres collected in 60 seconds is 8.33 L/s.
Where is flow rate used in daily life?
Sizing water pumps for overhead tanks, irrigation pipes, filter pumps and industrial pipelines all start from the required flow rate, so this calculation avoids buying an undersized pump.
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