Natural Gas Cost Formula — Therm, CCF, MCF Conversions

Natural gas is billed in therms, CCF (100 cubic feet), or MCF (1,000 cubic feet) depending on the utility and contract. Each unit has a fixed energy content under standard conditions, but heating values vary by composition. Translating gas usage and rates between units is the first step in any procurement comparison, fuel-switching study, or fuel-cost budget — and getting the conversion wrong silently misstates the answer.

Overview

A therm is exactly 100,000 BTU of energy — an energy unit. A CCF is 100 cubic feet of natural gas at standard conditions — a volumetric unit. The two convert via the heating value of the gas, typically about 1,030 BTU/scf, so 1 CCF ~ 1.037 therms. An MCF is 1,000 cubic feet, so 1 MCF ~ 10.37 therms. The exact factor changes with gas composition: a wet, high-BTU gas can carry 1,100+ BTU/scf, while a lean dry gas with N₂ dilution can be 950 BTU/scf.

Utility bills typically separate a fixed customer charge from a volumetric supply charge and (in unbundled markets) a transportation or LDC charge. A gas-vs-electric heating comparison uses the BTU-per-dollar metric on each side, adjusted for the furnace or appliance efficiency.

Theory

All energy comparisons go through BTU. A residential gas furnace delivers ~95% of input BTU to space heat (AFUE = 0.95). Electric resistance heaters deliver ~100%. Heat pumps deliver ~250–400% (COP 2.5–4) of input electric energy. Translating between billed units (therms, CCF, MCF, kWh) and delivered BTU is the basis of any fuel-switching decision.

Formulas

Unit Conversions

1 therm = 100,000 BTU = 29.3001 kWh = 105.506 MJ
1 CCF   = 100 scf  ~ 1.037 therms     (at HHV = 1037 BTU/scf)
1 MCF   = 1000 scf ~ 10.37 therms     (at HHV = 1037 BTU/scf)
1 MMBtu = 10 therms = 1,000,000 BTU
1 dekatherm (Dth) = 10 therms = 1 MMBtu

CCF to Therms (Variable Heating Value)

therms = CCF * (HHV / 1000)

HHV (typical, lean dry gas)   = 1000 BTU/scf
HHV (typical, residential)    = 1030 - 1050 BTU/scf
HHV (rich wet gas / NGL-rich) = 1050 - 1150 BTU/scf
HHV (N2-diluted gas)          = 900 -  990 BTU/scf

Utilities publish a billing-period BTU factor (sometimes called pressure factor or heat content adjustment). Use the published factor where available.

Gas Bill (LDC Billing Structure)

Bill_total = Fixed_charge + Supply_charge + Transport_charge

Supply_charge   = usage_therms * supply_rate ($/therm)
Transport_charge = usage_therms * transport_rate ($/therm)  [unbundled markets]

Monthly_cost = Bill_total
Yearly_cost  = sum(Bill_total over 12 months)

Gas-vs-Electric Cost per Delivered BTU

Cost per delivered BTU (gas):
  $_per_BTU_gas = supply_rate / (100000 * AFUE_furnace)

Cost per delivered BTU (electric resistance):
  $_per_BTU_elec = elec_rate / 3412.14

Cost per delivered BTU (heat pump):
  $_per_BTU_HP = elec_rate / (3412.14 * COP)

elec_rate in $/kWh; 1 kWh = 3412.14 BTU

Equivalent Electric Cost for Same Delivered Heat

Q_delivered (BTU) = usage_therms * 100000 * AFUE_furnace

Equivalent_elec_cost ($) = Q_delivered / 3412.14 * elec_rate  (resistance)
Equivalent_elec_cost ($) = Q_delivered / (3412.14 * COP) * elec_rate  (heat pump)

Key Symbols

Symbol	Description	Units
therm	Energy = 100,000 BTU	BTU
CCF	100 cubic feet at standard conditions	scf
MCF	1000 cubic feet at standard conditions	scf
HHV	Higher heating value	BTU/scf
AFUE	Annual fuel utilization efficiency (furnace)	fraction
COP	Coefficient of performance (heat pump)	dimensionless

Worked Example

Given: Monthly usage = 80 CCF, supply rate = $1.20/therm, fixed charge = $12/month, electric rate = $0.13/kWh, furnace AFUE = 0.95, electric resistance for comparison.

Step 1 — Convert CCF to therms (HHV = 1030 BTU/scf):

therms = 80 * (1030 / 1000) = 82.4 therms

Step 2 — Monthly gas bill:

Supply_charge = 82.4 * 1.20 = $98.88
Bill = $12 + $98.88 = $110.88 per month
Yearly = $110.88 * 12 = $1330.56

Step 3 — Delivered BTU:

Q_delivered = 82.4 * 100000 * 0.95 = 7,828,000 BTU

Step 4 — Equivalent electric (resistance) cost:

Equivalent_kWh = 7,828,000 / 3412.14 = 2294 kWh
Equivalent_elec_cost = 2294 * 0.13 = $298.22 per month
Yearly_elec_equiv = $298.22 * 12 = $3578.65

Reading: Gas heating at $1.20/therm and 95% AFUE delivers the same heat as electric resistance at less than 40% of the cost. A heat pump with COP = 3 would deliver the same heat at $99.41/month — effectively at parity with gas. The decision flips with the COP and electric rate.

Valid Ranges & Notes

Parameter	Typical Range
HHV (residential billing)	1020 – 1050 BTU/scf
US residential supply rate	$0.80 – $2.50 per therm
US residential electric rate	$0.10 – $0.35 per kWh
Modern furnace AFUE	0.80 – 0.98
Heat pump COP (heating)	2.5 – 4.0

When the formula is not enough

Tiered rates — many utilities apply different rates above usage thresholds. Use a piecewise rate model.
Seasonal supply-rate adjustments — winter rates are typically higher; monthly cost differs from annualized average.
Demand charges (commercial / industrial) — peak hourly use drives a separate charge not captured in volumetric rate.
Hedged supply contracts — effective rate combines a fixed hedge price with a spot exposure; use blended rate.
Heat pump COP varies with outdoor temperature — use bin-hour analysis for cold climates, not a single COP.

References

U.S. Energy Information Administration (EIA) — Natural Gas Conversion Factors and Heating Values: https://www.eia.gov
American Gas Association (AGA) — Natural Gas Heating Content Standards.
DOE Building Technologies — Furnace AFUE Standards (10 CFR Part 430): https://www.energy.gov
U.S. EPA ENERGY STAR — Heat Pump COP Ratings.
GPSA Engineering Data Book, 13th ed., Section 1 (General Information).