Gas bills use the word therm, but most people do not know what it means. Unlike electricity, gas is not billed in something familiar like kilowatt-hours.
This page is part of the Gas Bill Explained guide, which breaks down every section of a typical U.S. gas bill in plain English.
Because therms are confusing, many people do not understand why their gas bill changes from month to month.
This page explains what a therm is, how it is calculated, and why it matters on your gas bill.
A therm is a unit that measures heat energy.
- 1 therm = 100,000 BTUs (British Thermal Units)
- Utilities use therms so customers are billed for the actual energy delivered, not just gas volume
Natural gas enters your home as a volume (often measured in CCF or Mcf). The utility converts that volume into therms using a heat-content factor.
How Therms Appear on Your Bill
Most gas bills follow this path:
Gas meter reading → volume (CCF or Mcf) → heat content factor → therms billed
This ensures fairness when gas quality varies slightly.
Control level: None
Find it on your bill: Usage, therm conversion, or heat content section
Examples
- Gas furnace uses 1 therm per hour → running 5 hours = 5 therms
- Gas water heater may use 15–25 therms per month
- Gas stove uses very little by comparison
A typical home may use:
- 20–40 therms/month in summer
- 80–150+ therms/month in winter
Summary
A therm measures how much heat energy you used, not how much gas volume passed through the meter. Understanding therms makes gas bills predictable, especially during winter.
Sources
U.S. Energy Information Administration – Natural Gas Units