How do I find the cross-sectional area of a round pipe?
Use A = π × r², where r is the inner radius. For a pipe with inner diameter d, the area is A = π × (d/2)² = π × d² / 4.
What is the difference between volumetric and mass flow rate?
Volumetric flow rate (m³/s or litres/min) measures the volume of fluid per unit time. Mass flow rate (kg/s) measures the mass per unit time. They are related by fluid density: ṁ = ρ × Q.
Can I use this as a quick pipe flow rate calculator?
Yes, if you already know the mean velocity and the true internal area or can derive it from diameter. The result is a quick continuity-equation screen, not a replacement for a full pressure-loss or pipe-sizing calculation.
Why does the calculator show equivalent circular diameter?
The equivalent circular diameter helps you interpret the same area as a round pipe size. That makes the answer easier to compare against common pipe diameters even when the flow path is not perfectly round.
What density should I enter?
Use the fluid density for the actual fluid and temperature when you need mass flow. Water is a good default for water service screens, air is useful for rough gas planning, and light oil can be a helpful comparison for lower-density liquids.
What does GPM mean in a flow rate calculator?
GPM means gallons per minute. It is a common pump and plumbing label, especially in North America. The tricky part is that not every source means the same gallon size, so this page shows both US gallons per minute and Imperial gallons per minute alongside litres per minute and cubic metres per hour.
How do I estimate how long it will take to fill a tank?
Use the inverse of flow rate: fill time = volume / flow rate. If you know the tank volume in litres or cubic metres and the flow rate in litres per minute, litres per second, or cubic metres per hour, you can convert the time to seconds, minutes, or hours. The calculator’s fill-time table gives you common planning volumes without needing to do that rearrangement yourself.
Can I use this calculator to size a pipe?
You can use it as a starting point, but not as a full pipe-sizing tool. The equivalent circular diameter helps you compare the area with a round pipe size, yet real pipe sizing also needs pressure loss, fitting losses, roughness, elevation, and the acceptable velocity for the fluid. If you already know pipe diameter and want velocity, a pipe-velocity calculator or water-velocity calculator is usually the better next step.
Why does the calculator show both litres per minute and gallons per minute?
Because different industries use different labels. Water treatment, plumbing, and process work often use litres per minute or cubic metres per hour, while pumps and older specs often use gallons per minute. Showing both makes the same flow easier to compare across documents without manual conversion.
What is the difference between volumetric flow rate and mass flow rate?
Volumetric flow rate measures the amount of fluid volume moving each second, minute, or hour. Mass flow rate measures how much mass is moving in the same time. If you know density, the calculator can convert between them with mass flow = volumetric flow × density.
Is the equivalent circular diameter the same as pipe diameter?
It is a comparison diameter, not a promise that the channel is actually round. The calculator converts area into the diameter of a circle with the same cross-sectional area, which is handy for comparison and rough sizing. Real pipe selection still needs pressure-loss and velocity checks.
Should I use litres per minute or cubic metres per hour?
Use the unit that matches the document or equipment you are comparing against. Litres per minute is common for smaller flows and quick pump checks, while cubic metres per hour is often easier on process sheets and larger plant references. They are the same flow expressed at different scales.
Does fluid density change the volumetric flow result?
No. Density changes the mass flow result, not the volumetric flow result. The continuity equation uses area and velocity for volumetric flow, then density is applied to translate that flow into kilograms per second or kilograms per minute.
Can I use this for air as well as water?
Yes, as a planning tool. The continuity equation works for any fluid, but the calculator assumes incompressible, steady flow. That is a good approximation for many low-speed liquid and gas checks, but high-speed gas flow or strongly compressible systems need a more specialised model.
