What exactly is a therm?

A therm is defined as exactly 100,000 BTU, the standard billing unit for natural gas in the US. 1 therm = 29.3 kilowatt-hours of heat content. It's roughly the energy released by burning one 'unit' of natural gas, making it intuitive for residential billing.

Why does my gas bill show therms instead of kilowatt-hours like electricity?

Historical convention. Natural gas utilities adopted the therm early as a standard unit (before kWh became universal). Unlike electricity, gas delivery is harder to meter precisely in real-time, so therms (large, round numbers) made consumer bills simpler and less confusing.

My furnace is rated 100,000 BTU/hour. How many therms is that?

Exactly 1 therm per hour. Since 1 therm = 100,000 BTU, a 100,000 BTU/hour furnace burns exactly 1 therm per hour of continuous operation. For a 24-hour day: 24 therms, or ~2,532,000 kJ.

How do I compare natural gas and electricity costs?

Convert both to the same unit (kJ or kWh). 1 therm = 29.3 kWh (105,500 kJ). If gas costs $1.00/therm and electricity costs $0.15/kWh, gas is cheaper per unit energy. But factor in furnace efficiency (80–98%) versus electric heating (nearly 100%).

Kilojoules (kJ) to Therms (US) Converter

Enter a value to instantly convert between energy units.

From

Precision4 dp

1 Kilojoule = 0 Therm (US)

Key Formulas

Kilocalorie → Kilojoule

kJ = kcal × 4.184

Kilojoule → Kilocalorie

kcal = kJ × 0.239006

Kilowatt-Hour → Joule

J = kWh × 3600000

Joule → Kilowatt-Hour

kWh = J × 2.77778e-7

Formula

thm = kJ ÷ 105500

A therm is a US unit of natural gas billing — it represents 100,000 BTU, roughly the energy content in one of natural gas burned. Kilojoules are SI units. You need this conversion when reviewing natural gas utility bills (billed in therms), sizing a furnace or water heater (capacity often quoted in therms or BTU), or comparing home heating energy between gas and electricity. One therm equals about 105.5 megajoules — a huge amount of energy in metric terms, reflecting the high energy density of natural gas.

Source: NIST SP 811, Table B.8

Frequently Asked Questions

Real-World Examples

A homeowner reviewing a natural gas bill. Their usage: 1 therm = 105,500 kJ of natural gas burned for heating. At $1.20/therm, that therm cost $1.20.

105500 kJ = 1 thm

An HVAC installer sizing a furnace for a home. Customer needs 5 therms/day winter capacity = 528,750 kJ/day. This specifies a furnace that delivers ~60,000 BTU/hour continuously.

528750 kJ = 5 thm

A commercial kitchen calculating natural gas demand. Water heater consumes 2 therms/month (211,000 kJ/month) during winter; summer drops to 0.5 therms due to lower hot-water demand.

211000 kJ = 2 thm

A utility auditor comparing homes. House A used 30 therms last month (3,165,000 kJ); House B used 24 MWh electricity. Converting both to kJ shows House A's total heating was more efficient for that season.

3165000 kJ = 30 thm

kcal to kj kj to kcal kwh to joules joules to kwh btu to joules calories to joules

Kilojoules (kJ) to Therms (US) Converter

Key Formulas

Formula

Frequently Asked Questions

Real-World Examples

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