Megatons of TNT to Therm (US)

One megaton equals 4.184 × 10¹⁵ joules — the energy of burning about 120 million liters of petrol or the total electricity output of a large power plant running for 50 days. A 1-megaton airburst would flatten reinforced concrete buildings within 2 km, cause third-degree burns at 10 km, and break windows at 40+ km. It is roughly 67 times the Hiroshima bomb.

The Soviet AN602 "Tsar Bomba," detonated on 30 October 1961, yielded approximately 50 megatons — the largest human-made explosion in history. It was a three-stage thermonuclear device originally designed for 100 Mt but scaled down by replacing the uranium tamper with lead to reduce fallout. The fireball was 8 km wide, and the mushroom cloud rose 67 km. It was a propaganda weapon with no practical military use.

Modern strategic warheads are smaller than Cold War designs because accuracy improved. The US W88 yields about 0.475 Mt; the W76-1 about 0.1 Mt. Russian RS-28 Sarmat MIRVs carry warheads estimated at 0.5–0.8 Mt each. Military planners found that several smaller warheads (MIRVs) destroy more area than one large one due to the cube-root scaling of blast radius with yield.

The Chicxulub impact that ended the dinosaurs released roughly 100 million megatons (10²³ J). The Tunguska event (1908) was 3–15 megatons. NASA's planetary defense threshold is objects capable of 1+ megatons of damage. A 50-meter iron asteroid striking Earth at 20 km/s would release about 10 megatons — enough to obliterate a major city.

Accuracy replaced raw yield. A 0.5 Mt warhead landing within 100 meters of a target destroys it just as effectively as a 10 Mt warhead landing 1 km away. MIRVed missiles carrying 6–10 smaller warheads also cover more total area than one massive bomb. The US retired its last megaton-class warhead (the B83) in 2022, relying entirely on sub-megaton weapons.

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.