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CNG Fill Quantity Calculator

Work out cng fill quantity instantly with clear inputs, formula shown and shareable results.

About CNG Fill Quantity Calculator

CNG mass follows the real gas law m = pV / (Z R T), with R for methane of 0.5183 kJ/kg.K. Compressibility Z falls to around 0.85 at 200 bar, so ideal-gas arithmetic overstates the fill by 15%. Temperature matters greatly: a hot fill loses mass as the gas cools and pressure settles.

Formulas

Real gas mass

m = p V / (Z R T), with R = 0.5183 kJ/kg.K for methane

Equivalents

Nm3 = mass / 0.717; GGE = mass / 2.567 kg

Worked example

With the default values below, CNG Fill Quantity Calculator returns Gas Mass In Cylinder of 8.737. Change any input above and every figure here is recalculated in your browser.

Inputs used

Cylinder Water Volumeminimum 0.01 L
60 L
Fill Pressureminimum 0.01 bar
200 bar
Gas Temperatureminimum -50 degrees C
35 degrees C
Compressibility Factor Zaccepts 0.1–1.5
0.86

Results

Gas Mass In Cylinder
8.737
Volume At Normal Conditions
12.185
Gasoline Gallon Equivalent
3.403
Energy Content
432.46

Step by step

  1. 1Values used
  2. 2Real gas mass
  3. 3Equivalents
  4. 4Gas Mass In Cylinder= 8.737
  5. 5Volume At Normal Conditions= 12.185
  6. 6Gasoline Gallon Equivalent= 3.403
  7. 7Energy Content= 432.46

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • CNG is stored at very high pressure. Cylinders must be within their certification period and filling must follow the applicable gas cylinder safety standard.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

CNG is stored at very high pressure. Cylinders must be within their certification period and filling must follow the applicable gas cylinder safety standard.

Frequently Asked Questions

Why does a fast fill deliver less gas?

Compression heats the gas, so the cylinder reaches target pressure at high temperature with less mass inside. As it cools, pressure drops and the tank reads part-full. Temperature-compensated fill controls correct for this.

What is a gasoline gallon equivalent?

The mass of CNG with the same energy as one US gallon of gasoline, about 2.567 kg. It allows CNG to be priced comparably to liquid fuels.

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