Conversion Formula
One therm is exactly 100,000 BTU, which equals 29.3001 kWh. This is the standard billing unit for natural gas in the United States and the United Kingdom.
Complete Guide to Therms to Kilowatt-hours Conversion
What is a Therms?
A therm is a unit of heat energy equal to 100,000 BTU. Gas utilities in the US and UK bill in therms because the energy content of a given volume of gas varies with its composition.
What is a Kilowatt-hours?
A kilowatt-hour (kWh) is one kilowatt sustained for one hour and the universal unit of electricity billing, battery capacity and solar production.
How the Conversion Works
Because one BTU is 1,055.06 J and one kWh is 3,600,000 J, 100,000 BTU works out to 29.3001 kWh. Gas meters measure volume; the utility multiplies by a calorific value to arrive at therms, then bills that figure.
Why This Conversion Matters
The gas-versus-heat-pump decision is the single largest energy choice most households make. It can only be evaluated once gas therms and electric kilowatt-hours sit in the same unit and both are adjusted for appliance efficiency.
Scientific Context
Natural gas calorific value typically ranges from 37 to 43 MJ per cubic metre depending on methane content. Utilities publish this figure on each bill, which is why the same volume of gas can produce slightly different therm readings month to month.
Step-by-Step Conversion Guide
Follow these steps to convert therms to kilowatt-hours manually:
Start with your value in therms
Example: You want to convert 5 thm
Apply the conversion formula
Use the formula: kWh = therms × 29.3001
Calculate the result
5 thm = 146.5005 kWh
Verify your answer
Use our calculator above to double-check your manual calculation.
Quick Mental Math Tip
One therm is exactly 100,000 BTU, which equals 29.3001 kWh. This is the standard billing unit for natural gas in the United States and the United Kingdom.
Common Conversions
| Therms (thm) | Kilowatt-hours (kWh) | Kilowatt-hours → Therms |
|---|---|---|
| 1 | 29.3001 | 1 kWh = 0.0341 thm |
| 2 | 58.6002 | 2 kWh = 0.0683 thm |
| 5 | 146.5005 | 5 kWh = 0.1706 thm |
| 10 | 293.001 | 10 kWh = 0.3413 thm |
| 20 | 586.002 | 20 kWh = 0.6826 thm |
| 30 | 879.003 | 30 kWh = 1.0239 thm |
| 50 | 1465.005 | 50 kWh = 1.7065 thm |
| 75 | 2197.5075 | 75 kWh = 2.5597 thm |
| 100 | 2930.01 | 100 kWh = 3.413 thm |
| 250 | 7325.025 | 250 kWh = 8.5324 thm |
| 500 | 14650.05 | 500 kWh = 17.0648 thm |
When You'll Need This Conversion
Gas versus heat pump decisions
Convert your gas bill into kWh to compare it directly against electric heating costs.
Building energy benchmarking
Normalise mixed-fuel buildings into a single energy metric per square metre.
Boiler replacement sizing
Translate annual therm consumption into the kW heat demand a replacement system must meet.
Energy literacy
Understand what a utility statement actually charges for.
Pro Tips for Accurate Conversions
Always adjust for efficiency
Multiply gas kWh by boiler efficiency (0.85–0.94) to get delivered heat before comparing with a heat pump.
Use a whole heating season
Single-month comparisons are distorted by weather. Twelve months of therms gives a usable baseline.
Check the calorific value on your bill
It shifts by a few percent between suppliers and seasons, which changes your therm total.
Common Mistakes to Avoid
Comparing gas and electricity unit prices directly
A therm contains 29.3 times the energy of a kWh, so gas always appears cheaper per unit.
Convert to a common unit, then divide by appliance efficiency or COP.
Assuming 100% boiler efficiency
Even condensing boilers lose 6–15% of the gas energy up the flue.
Use the appliance efficiency rating printed on the unit.
Ignoring standing charges
Fixed daily gas charges continue even after switching most heating to electricity.
Include standing charges in any switching calculation.
History & Background
The therm was introduced to bill gas by energy content rather than volume after gas composition became variable with the shift from town gas to natural gas.
Key Milestones
The therm is defined as 100,000 BTU for gas trading.
The UK converts from town gas to North Sea natural gas, making energy-content billing essential.
US utilities adopt therm billing broadly following gas price deregulation debates.
Heat pump adoption drives mass conversion of therms into kWh for cost comparison.
Global Usage Today
Therms are used in US and UK gas billing. Continental Europe bills gas in kWh directly, and Australia uses megajoules.
Frequently Asked Questions
Related Guides & Articles
View allMetric vs Imperial: The Complete Guide to Measurement Systems
The world is divided between two major measurement systems: metric and imperial. Understanding the d...
The Fascinating History of Temperature Scales
Temperature is something we experience every day, yet the scales we use to measure it have fascinati...
The International System of Units (SI): The Language of Science
The International System of Units (SI) is the modern metric system and the world most widely used sy...
The Complete Guide to Unit Conversion: From Basics to Mastery
Unit conversion is the essential skill that bridges the gap between different measurement systems. W...
Want to learn more about energy conversions?
Browse all energy articles →People Also Convert
Related calculators users frequently visit alongside therms to kilowatt-hours.
Last verified: April 2026. All conversion factors are based on internationally defined standards.