Kilojoule to Therm (US)

Australia, New Zealand, and the EU mandate SI-based labeling, so food packages list energy in kilojoules. The US and Canada stuck with kilocalories (branded as "Calories"). To convert, divide kJ by 4.184 — a 500 kJ snack bar is about 120 kcal. Most Australian shoppers learn the kJ scale by familiarity rather than converting every time.

A 70 kg person walking briskly at 5.5 km/h burns roughly 600–700 kJ in 30 minutes (about 150–170 kcal). That is roughly one banana or a small flat white. Running the same distance roughly triples the kilojoule burn because the body must lift itself off the ground with every stride.

They measure the same thing — food energy — in different units. One kilocalorie (kcal) equals 4.184 kilojoules (kJ). European and Australian labels show both; US labels show only kcal (labelled "Calories"). A 2,000 kcal/day diet is 8,368 kJ/day. Nutritionists consider the two interchangeable for dietary guidance.

A typical smartphone battery rated at 15 Wh holds about 54 kJ. That is roughly the food energy in a single sugar cube (17 kJ per cube times three). A laptop battery at 60 Wh stores about 216 kJ, and a Tesla Model 3 battery pack at 60 kWh stores 216,000 kJ — enough dietary energy to feed a person for about 25 days.

It is a middle-ground unit — too large for electronics (which use millijoules) and too small for household energy bills (which use megajoules or kWh). One kilojoule is the kinetic energy of a tennis ball served at about 160 km/h, the energy in a small sip of juice, or the heat generated by a 100 W bulb in ten seconds. It sits at the human snack-and-exercise scale.

Residential US natural gas prices typically range from $0.80 to $2.50 per therm depending on region, season, and utility. The wholesale Henry Hub benchmark translates to about $0.25 per therm at $2.50/MMBtu. Delivery charges, taxes, and utility markups roughly triple or quadruple the commodity cost by the time it reaches a home meter.

The average US home using gas for heating consumes about 500–900 therms per year, depending on climate, insulation, and home size. Homes in mild climates like Southern California may use under 300 therms; homes in Minnesota or Wisconsin can exceed 1,200 therms. Gas water heaters alone account for roughly 150–250 therms per year.

One US therm equals exactly 100,000 BTU, while one MMBtu (million BTU) equals 1,000,000 BTU — so 1 MMBtu equals 10 therms. Wholesale gas markets and pipeline contracts use MMBtu; residential utility bills use therms. The two are straightforward to convert, but confusing them by a factor of ten is a common mistake in energy cost comparisons.

Retail billing in therms gives homeowners manageable numbers — a winter month might be 80–120 therms at $1–2 each. Wholesale pipeline contracts deal in millions of BTU (MMBtu) because the volumes are enormous and the industry standardized on BTU-based pricing in the early 20th century. One MMBtu equals 10 therms, so converting is simple. The Henry Hub benchmark price of $2.50/MMBtu translates to about $0.25/therm before delivery charges, taxes, and utility markup roughly quadruple it at the meter.

A typical US residential furnace rated at 80,000–100,000 BTU/h uses about 0.8–1.0 therms per hour at full output. High-efficiency condensing furnaces (95%+ AFUE) extract more heat per therm, so they cycle less often. On a cold winter day, a furnace might run 8–12 hours total, consuming 6–10 therms. That translates to roughly $5–$25 per day depending on local gas prices.