Therm (US) to Tons of TNT

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.

One ton of TNT releases 4.184 GJ — roughly the energy of 120 liters of petrol or the electricity an average US home uses in 1.2 days. In blast terms, one ton of TNT in open air produces lethal overpressure within about 15–20 meters and can shatter windows at 100+ meters. The MOAB bomb (11 tons TNT) flattened structures across a 150-meter radius.

They differ by factors of 1,000: 1 kiloton = 1,000 tons, 1 megaton = 1,000,000 tons. Conventional bombs are rated in tons (the MOAB is 11 tons). Tactical nuclear weapons are rated in kilotons (Hiroshima was ~15 kt). Strategic thermonuclear warheads are rated in megatons (modern US warheads are 0.3–0.475 Mt). The scale spans nine orders of magnitude.

The 2020 Beirut explosion was caused by 2,750 tonnes of ammonium nitrate and was estimated at roughly 500–1,100 tons of TNT equivalent. For comparison, the Oklahoma City bombing (1995) was about 2 tons TNT equivalent, and the Halifax explosion (1917) was roughly 2,900 tons. Beirut ranked among the largest non-nuclear explosions in history.

Small meteor airbursts are rated in tons or kilotons of TNT. The 2013 Chelyabinsk meteor released about 440,000 tons (440 kt) — roughly 30 times the Hiroshima bomb. The Tunguska event (1908) is estimated at 3–15 megatons. The Chicxulub asteroid that ended the dinosaurs released roughly 100 trillion tons (100 million megatons) of TNT equivalent energy.

The largest planned non-nuclear explosion was the British demolition of Heligoland fortifications in 1947, using 6,700 tons of TNT equivalent. The largest accidental explosion was the Halifax harbour disaster (1917) at roughly 2,900 tons. The largest conventional bomb, the US GBU-43/B MOAB, yields about 11 tons — tiny compared to accidental industrial blasts.