Quick Answer: Therms to Kilowatt-hours
One therm equals 29.307107 kilowatt-hours (1 thm = 29.307107 kWh).
Conversely, 1 kWh = 0.0341214163 thm.
Formula: kWh = therms (US) × 29.307107
Worked examples
- 1 thm = 29.307107 kWh
- 2 thm = 58.614214 kWh
- 5 thm = 146.535535 kWh
Method and limitations
This page uses the US therm: exactly 100,000 International Table BTU, which is 100,000 × 1,055.05585262 J = 29.307107 kWh. US gas utilities bill in therms. The UK therm used on older British gas bills is defined as 105,506,000 J = 29.307222 kWh — a difference of four parts per million, immaterial for billing but worth naming rather than leaving ambiguous. Multiply therms by 29.307107 for the US figure. Calculations use full-precision constants; displayed values are rounded to at most 9 significant figures. Results are rounded for display only. Full precision is kept internally, so long chains of conversions do not accumulate rounding error. Where US customary and imperial units share a name (for example fluid ounces and gallons), this page uses the US customary definition and says so explicitly.
Each factor is exact by definition, derived from exact definitions, or a documented conventional value — see the methodology and sources.
Conversion Formula
This page uses the US therm: exactly 100,000 International Table BTU, which is 100,000 × 1,055.05585262 J = 29.307107 kWh. US gas utilities bill in therms. The UK therm used on older British gas bills is defined as 105,506,000 J = 29.307222 kWh — a difference of four parts per million, immaterial for billing but worth naming rather than leaving ambiguous. Multiply therms by 29.307107 for the US figure.
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(IT) works out to 29.307107 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 (US) × 29.307107
Calculate the result
5 thm = 146.5355 kWh
Verify your answer
Use our calculator above to double-check your manual calculation.
Quick Mental Math Tip
This page uses the US therm: exactly 100,000 International Table BTU, which is 100,000 × 1,055.05585262 J = 29.307107 kWh. US gas utilities bill in therms. The UK therm used on older British gas bills is defined as 105,506,000 J = 29.307222 kWh — a difference of four parts per million, immaterial for billing but worth naming rather than leaving ambiguous. Multiply therms by 29.307107 for the US figure.
Common Conversions
| Therms (thm) | Kilowatt-hours (kWh) | Kilowatt-hours → Therms |
|---|---|---|
| 1 thm | 29.3071 | 1 kWh = 0.0341214 thm |
| 2 thm | 58.6142 | 2 kWh = 0.0682428 thm |
| 5 thm | 146.536 | 5 kWh = 0.170607 thm |
| 10 thm | 293.071 | 10 kWh = 0.341214 thm |
| 20 thm | 586.142 | 20 kWh = 0.682428 thm |
| 30 thm | 879.213 | 30 kWh = 1.02364 thm |
| 50 thm | 1,465.36 | 50 kWh = 1.70607 thm |
| 75 thm | 2,198.03 | 75 kWh = 2.55911 thm |
| 100 thm | 2,930.71 | 100 kWh = 3.41214 thm |
| 250 thm | 7,326.78 | 250 kWh = 8.53035 thm |
| 500 thm | 14,653.6 | 500 kWh = 17.0607 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
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Conversion factors on this page are either exact by definition, derived from exact definitions, or conventional values in documented use. Each is listed with its source in our conversion methodology and sources, which cites the BIPM SI Brochure, NIST Special Publication 811 and the relevant IEC or national standards. Results are rounded for display only; calculations use full precision.