Calculate natural gas pipe flow rate, diameter, or velocity from any 2 values with unit conversions for m³/s, ft³/s, m/s, and ft/s.
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Natural Gas to Velocity Formula
The calculator uses the circular pipe flow relationship between volumetric flow rate, internal pipe diameter, and gas velocity. It converts all inputs to base units first: flow rate in m³/s, diameter in meters, and velocity in m/s.
A = pi*(D/2)^2
V = Q/A
Q = V*A
D = sqrt((4*Q)/(pi*V))
- A = internal cross-sectional area of the pipe
- Q = volumetric flow rate of natural gas
- V = natural gas velocity
- D = internal diameter of the natural gas pipe
- pi = 3.14159265…
If you enter flow rate and pipe diameter, the calculator solves for velocity using V = Q / A. If you enter diameter and velocity, it solves for flow rate using Q = V × A. If you enter flow rate and velocity, it solves for the required internal diameter using D = √((4Q) / (πV)).
The result is based on volumetric flow through a round pipe. It does not adjust for pressure, temperature, gas compressibility, pipe roughness, fittings, or pressure drop.
Natural Gas Velocity and Unit Reference
The table below gives general velocity ranges for interpreting a result. Actual acceptable velocity depends on pipe material, allowable pressure drop, noise limits, local codes, and system design requirements.
| Velocity Range | Approx. ft/s | General Interpretation |
|---|---|---|
| Less than 5 m/s | Less than 16.4 ft/s | Low velocity, often associated with lower pressure loss |
| 5 to 15 m/s | 16.4 to 49.2 ft/s | Common design range for many fuel gas piping checks |
| 15 to 30 m/s | 49.2 to 98.4 ft/s | Higher velocity, pressure drop and noise should be checked carefully |
| Greater than 30 m/s | Greater than 98.4 ft/s | Very high for many systems, usually needs engineering review |
These are the unit conversions used for the supported inputs and outputs.
| Quantity | Unit | Conversion to Base Unit |
|---|---|---|
| Flow rate | L/s | 1 L/s = 0.001 m³/s |
| Flow rate | ft³/s | 1 ft³/s = 0.0283168 m³/s |
| Diameter | in | 1 in = 0.0254 m |
| Diameter | ft | 1 ft = 0.3048 m |
| Velocity | ft/s | 1 ft/s = 0.3048 m/s |
Example Calculations
Example 1: Calculate natural gas velocity
You have a volumetric flow rate of 0.10 m³/s through a pipe with an internal diameter of 0.10 m.
A = pi*(0.10/2)^2 = 0.007854 m^2
V = 0.10/0.007854 = 12.732 m/s
The natural gas velocity is about 12.73 m/s.
Example 2: Calculate required pipe diameter
You have a flow rate of 50 L/s and want a gas velocity of 8 m/s. First convert the flow rate:
50 L/s = 0.050 m^3/s
D = sqrt((4*0.050)/(pi*8)) = 0.0892 m
The required internal diameter is about 0.0892 m, or 8.92 cm.
FAQs
Does this calculate standard or actual natural gas velocity?
It calculates velocity from the volumetric flow rate you enter. If your flow rate is actual m³/s at the pipe conditions, the velocity result is actual velocity. If your flow rate is a standard flow value corrected to standard temperature and pressure, you need to convert it to actual pipe conditions before using it for actual velocity.
Should I use nominal pipe size or internal diameter?
Use the internal diameter. Nominal pipe size is not always the same as the inside diameter, especially when wall thickness changes. A small difference in diameter can cause a noticeable difference in velocity because area depends on diameter squared.
Why does velocity increase when the pipe diameter gets smaller?
For the same volumetric flow rate, a smaller pipe has less cross-sectional area. Since velocity equals flow rate divided by area, reducing the area increases the velocity.
