# Formulas

## Volumes

Formulas:

Mcf = 1,000Cf
MMcf = 1,000Mcf or 1,000,000Cf
Bcf = 1,000Mmcf or 1,000,000Mcf or 1,000,000,000Cf
Bbl = 42 Gal

Calculation Examples:

150,000 Mcf = 150 MMcf (150,000 divided by 1,000)
150,000 Mcf = .150 Bcf (150,000 divided by 1,000 divided by 1,000)
1.275 Bcf = 1,275 MMcf (1.275 times 1,000)
1.275 Bcf = 1,275,000 Mcf (1.275 times 1,000 times 1,000)

## Heating

The heating value of a volume of natural gas is determined by multiplying the Mcf volume times the appropriate Btu factor.

Btu factors are either presented as Btu per Cf or Btu per Mcf. If the Btu factor has 3 or 4 places to the left of the decimal point (for example, 1125.5 or 985.5), then the Btu factor is presented as Btu per Cf. If the Btu factor has 0 or 1 places to the left of the decimal (for example, 1.1255 or 0.9855), then the Btu factor is presented as Btu per Mcf.

General Rule:

Both the Mcf volume and the Btu Factor must be stated at the same conditions of pressure base and temperature and the Btu factor must be computed so as to derive the correct heating value based on whether the gas is dry or saturated.

Formulas:

MBtu = 1,000Btu (note: MBtu is not commonly used)
MMBtu = 1,000Mbtu or 1,000,000Btu
Btu per Mcf = Btu per Cf divided by 1,000
MMBtu = Mcf times Btu per Cf divided by 1,000 or Mcf times Btu per Mcf

Calculation Examples:

1,000Mcf times 1100 Btu/Cf divided by 1,000 = 1,100MMBtu
1,000Mcf times 1.100 Btu/Mcf = 1,100MMBtu

## Pressure Base

Natural gas volumes or Btu Factors (Heating Values) can be converted from one pressure base to another pressure base using the following formulas or conversion factors shown in Table 1 and Table 2 below.
General Rule: An MMBtu is an MMBtu regardless of the pressure base. Accordingly, as the pressure base increases, the natural gas volume (Mcf) decreases and the Btu Factor increases.

Formula Definitions:

PF = pressure base at which volume or Btu factor is being converted from
PT = pressure base at which volume or Btu factor is being converted to

Volume Conversion Formula:

Mcf@PF times (PF divided by PT) = Mcf@PT

Pressure Base Table 1

Conversion factors for converting Mcf volume from one pressure base to a different pressure base.

To Pressure Base of
From Pressure Base of14.6514.69614.7315.025
14.651.0000000.9968700.9945690.975042
14.6961.0031401.0000000.9976920.978103
14.731.0054611.0023141.0000000.980366
15.0251.0255971.0223871.0200271.000000

Heating Value Conversion Formula:

Volume Conversion Calculation Examples:
1000Mcf @14.65 times (14.65 divided by 14.73) = 995Mcf @14.73
1000Mcf @14.65 times .994569 = 995 Mcf @14.73

Btu@PF times (PT divided by PF) = Btu@PT

Pressure Base Table 2

Conversion factors for converting heating values (Btu factors) from one pressure base to a different pressure base. Note: the factors in Table 2 are the inverse (or reciprocals) of the factors shown in Table 1 (i.e. 1 divided by the Table 1 factor equals the Table 2 factor).

To Pressure Base of
From Pressure Base of14.6514.69614.7315.025
14.651.0000001.0031401.0054611.025597
14.6960.9968701.0000001.0023141.022387
14.730.9945690.9976921.0000001.020027
15.0250.9750420.9781030.9803661.000000

Heating Value Calculation Examples:

1010Btu/Cf @14.65 times (14.73 divided by 14.65) = 1016Btu/Cf @14.73
1010Btu/Cf @14.65 times 1.005461 = 1016Btu/Cf @14.73

## Dry Versus Saturated

Btu Factors (Heating Values) can be converted from Dry (natural gas not containing a significant amount of water) to Saturated (natural gas containing water) using the following formulas or conversion factors shown in Table 3. The .25636 factor used in the formulas and in the calculation of the table conversion factors is the vapor pressure of water at 60 degrees Fahrenheit as published in GPA Standard 2172-96.

General Rule:

A Btu is a Btu regardless of whether the gas is Dry or Saturated. Since water vapor will not burn or combust, natural gas of a given composition will contain fewer Btu per Cf if it is Saturated than it would contain if it were Dry. Consequently, the Btu Factor for Saturated gas is less than the Btu Factor for the same gas if it were Dry.

Formulas:

Btu/Cf-Sat divided by (1 minus (.25636 divided by Pb) = Btu/Cf-Dry
Btu/Cf-Dry times (1 minus (.25636 divided by Pb) = Btu/Cf-Sat

Dry vs. Saturated Table 3

Conversion factors for converting heating values from Dry to Saturated.

Pressure Base ofConversion Factor
14.650.982501
14.6960.982556
14.730.982596
15.0250.982938

Calculation Examples:

1000 Btu/Cf-Sat @14.65 divided by (1 minus (.25636 divided by 14.65) = 1018 Btu/Cf-Dry @14.65
1000 Btu/Cf-Sat @14.65 divided by .982501 = 1018 Btu/Cf-Dry @14.65

## NGL Gallons by Component

A volume of natural gas can be converted to its liquefiable hydrocarbon components (ethane, propane, etc) by using Mol% or GPM from the compositional analysis of the stream of natural gas.

Formula Definitions:

Cf/Mol = number of cubic feet in a Mol (see Note below)
Gal/#Mol = gallons per pound Mol

Note: The number of cubic feet in a Mol is pressure base sensitive. The standard per the Gas Processors Association is 379.49 cubic feet at a pressure base of 14.696. The formula to convert the standard to a different pressure base is as follows:

379.49 times (14.696 divided by PT)

NGL Gallons by Component Table 4
The number of cubic feet per Mol at different pressure bases

Pressure BaseCf/Mol Factor
14.65380.68157
14.696379.49000
14.73378.61406
15.025371.18037

NGL Gallons Table 5

The number of gallons per pound Mol by component

ComponentGal/#Mol
N2Nitrogen4.1643
CO2Carbon Dioxide6.4598
H2SHydrogen Sulfide5.1005
C1Methane6.417
C2Ethane10.123
C3Propane10.428
IC4Isobutane12.386
NC4Normal Butane11.9371
IC5Isopentane13.8595
NC5Normal Pentane13.7130
C6+Hexane+16.3920

Formulas:

Mcf times GPM for the component = Gallons
Mcf times [(Mol% divided by 100) divided by Cf/Mol] times 1000 times Gal/#Mol = Gallons

Calculation Examples:

1,000 Mcf @ 14.73 times 3.0088 GPM C2 = 3,009 Gallons of C2 (Ethane)
1000 Mcf @ 14.73 times [(11.25 Mol% C2 divided by 100) divided by 378.61406] times 1000 times 10.1259=3,009 Gallons of C2 (Ethane)

## MoI% to Gallons per Mcf

Compositional analysis of natural gas expressed as mol% can be converted into gallons per Mcf (GPM) factors by using the formulas and conversion factors shown in Tables 7, 8 and 9 below.

General Rule:

A gallon is a gallon regardless of pressure base.

Formula definitions:

Cf/Mol = number of cubic feet in a Mol (see Note below)
Gal/#Mol = gallons per pound Mol
Gal/Mcf = gallons per Mcf
GPM = gallons per Mcf
PF = pressure base to convert from
PT = pressure base to convert to

Note: The number of cubic feet in a Mol is pressure base sensitive. The standard per the Gas Processors Association is 379.49 cubic feet at a pressure base of 14.696. The formula to convert the standard to a different pressure base is as follows:

379.49 times (14.696 divided by PT)

Table 6

The number of cubic feet per Mol at different pressure bases

Pressure BaseCf/Mol Factor
14.65380.68157
14.696379.49000
14.73378.61406
15.025371.18037

Table 7

The number of gallons per pound Mol by component

Component Gal/#Mol
N2Nitrogen4.1513
CO2Carbon Dioxide6.4532
H2SHydrogen Sulfide5.1005
C1Methane6.4142
C2Ethane10.1259
C3Propane10.4327
IC4Isobutane12.3859
NC4Normal Butane11.9371
IC5Isopentane13.8595
NC5Normal Pentane13.7130
C6+Hexane+16.3920

Table 8

The number of gallons per thousand cubic feet (Mcf) at various pressure bases by component

Pressure Base
Component14.6514.69614.7315.025
N2Nitrogen10.904910.939110.964411.1840
CO2Carbon Dioxide16.951617.004817.044217.3855
H2SHydrogen Sulfide13.398413.440413.471513.7413
C1Methane16.849316.902216.941317.2806
C2Ethane26.599326.682826.744527.2801
C3Propane27.405427.491527.555128.1069
IC4Isobutane32.536132.638332.713833.3689
NC4Normal Butane31.357331.455731.528532.1599
IC5Isopentane36.407036.521336.605837.3389
NC5Normal Pentane36.022236.135336.218936.9442
C6+Hexane+43.059643.194843.294844.1619