Natural Gas BTU Calculator
Calculate energy content from gas composition.
About this calculator
Natural gas heating value is a composition-weighted average: each hydrocarbon component has its own standard heating value per cubic foot -- methane around 1,010 BTU/scf, ethane around 1,770, propane around 2,516, and butane around 3,262, values consistent with GPA/AGA reference tables -- while CO2 and nitrogen contribute zero heating value since they don't burn. This calculator normalizes the six entered percentages to sum to 100% before blending, so the composition doesn't need to add up perfectly on its own. Because methane typically makes up the large majority of a gas stream and its per-unit heating value is the lowest of the four combustible components, Methane has the largest measured effect on BTU per SCF of any input here -- but counterintuitively, in this normalized model, raising the Methane percentage while holding the other components' percentages fixed actually LOWERS BTU per SCF.
That happens because normalization rescales everyone to sum to 100%: pushing methane's share up proportionally shrinks the normalized share of the heavier, higher-BTU components (ethane, propane, butane) that were pulling the blended value above methane's own baseline. In practice this means the six percentages should be adjusted together to represent one real, physically sensible composition, not moved one at a time. Specific Gravity is computed from each component's molecular weight relative to air, and the Wobbe Index (heating value divided by the square root of specific gravity) is the standard figure gas utilities use to judge whether two gas supplies are interchangeable at existing burner equipment without needing to be re-tuned.
Inputs
Results
BTU per SCF
1,090 BTU
Total Energy
1,090.5 MMBtu
How to Use This Calculator
- Enter gas composition as percentages for methane (C1), ethane (C2), propane (C3), and butane (C4), plus CO2 and nitrogen.
- Enter the gas volume in Mcf (thousands of cubic feet).
- Read BTU per SCF, the heating value calculated from the hydrocarbon composition.
- Review Total Energy (MMBtu), which applies the heating value to the entered gas volume.
- Check Specific Gravity and Wobbe Index to assess gas quality and burner interchangeability.
How the result changes with Methane (C1)
| Methane (C1) | BTU per SCF | Total Energy |
|---|---|---|
| 43 | 1,149 BTU | 1,148.79 MMBtu |
| 64 | 1,112 BTU | 1,111.9 MMBtu |
| 100 | 1,080 BTU | 1,080 MMBtu |
What each input means
- Methane (C1)
- Percentage of methane in the gas stream.
- Ethane (C2)
- Percentage of ethane.
- Propane (C3)
- Percentage of propane.
- Butane (C4)
- Percentage of butane.
- CO2
- Percentage of carbon dioxide.
- Nitrogen
- Percentage of nitrogen.
- Gas Volume
- Volume of gas in thousands of cubic feet.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersMethane (C1) = 85, Ethane (C2) = 7, Propane (C3) = 3, Butane (C4) = 1 = 4 input(s) provided
- Calculate BTU per SCFBTU per SCF1090 = 1090
- Calculate Total EnergyTotal Energy1090.5 = 1090.5
- Calculate Specific GravitySpecific Gravity0.6588 = 0.6588
- Calculate Wobbe IndexWobbe Index1344 = 1344
Engine last updated . Checked against 1 independently-derived test — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does raising Methane % actually lower the calculated BTU per SCF?
This calculator normalizes all six entered percentages to sum to 100% before blending them, so raising Methane's raw percentage (while leaving the other five unchanged) proportionally shrinks their normalized share after rescaling. Since methane has the lowest per-unit heating value of the four combustible components, and the heavier hydrocarbons you're squeezing out have higher heating values, the blended result goes down -- not up. Adjust the other components alongside methane to represent one real, consistent gas composition.
Why do CO2 and Nitrogen contribute zero to the heating value?
CO2 and nitrogen are inert diluents in natural gas -- they don't combust, so they add no heat when the gas is burned. They do still count toward the total percentage used for normalization, and they lower the overall specific gravity and heating value per unit volume by displacing combustible gas, but their own component-level heating value contribution is zero.
What is the Wobbe Index used for?
The Wobbe Index (heating value divided by the square root of specific gravity) is the standard metric gas utilities and equipment manufacturers use to judge whether two different gas supplies will deliver essentially the same heat output through the same burner orifice without retuning. Two gases with different heating values and specific gravities can still have a similar Wobbe Index and behave similarly in existing appliances, which is why it's tracked separately from raw heating value.
Does the Gas Volume input change the BTU per SCF result?
No -- BTU per SCF depends only on the gas composition (the six percentage inputs), not on how much gas you have. Gas Volume is used separately to scale BTU per SCF up into Total Energy (in MMBtu) for the entered quantity of gas; it plays no role in determining the per-unit heating value itself.
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