TNT Equivalent Calculator (joules ↔ tons, kilotons, megatons of TNT)

Understanding the TNT equivalent calculator — concept and principle

The "ton of TNT" is a conventional unit for very large amounts of energy. This calculator converts an energy in joules, kilowatt-hours or other units into tonnes, kilotons and megatons of TNT, and back into joules, gigajoules, kWh and gigacalories. It is used to put meteor entries, volcanic eruptions, earthquakes or historic explosions on a common scale.

By convention one tonne of TNT is 4.184 GJ, so 63 TJ equals about 15 kilotons.

How it is calculated

Energy (J) = amount × unit factor

Tonnes of TNT = J ÷ 4.184×10⁹

Kilotons = J ÷ 4.184×10¹²; megatons = J ÷ 4.184×10¹⁵

kWh = J ÷ 3.6×10⁶

Unit factors: kJ 10³, MJ 10⁶, GJ 10⁹, TJ 10¹², PJ 10¹⁵, kWh 3.6×10⁶, MWh 3.6×10⁹, GWh 3.6×10¹², and the TNT units themselves.
One tonne of TNT is defined as exactly one gigacalorie (thermochemical calorie, 4.184 J).

The principle

The energy actually released by a tonne of real TNT varies a little with how it is measured, so scientists agreed on a fixed conventional value of 4.184 GJ. That makes the "ton of TNT" a pure energy unit, like the kilowatt-hour, and allows exact conversions. Saying an event released 15 kilotons does not mean TNT was involved; it means the energy equals that conventional amount. The unit tells you nothing about how fast the energy was released or what form it took, such as heat, blast or radiation.

Worked example

Default inputs: 63 terajoules (TJ), a figure commonly quoted for the 1945 Hiroshima explosion.

Energy = 63 × 10¹² = 63,000,000,000,000 J = 63,000 GJ.
Tonnes of TNT = 6.3×10¹³ ÷ 4.184×10⁹ = 15,060 t.
Kilotons = 15.06 kt; megatons = 0.01506 Mt.
kWh = 6.3×10¹³ ÷ 3.6×10⁶ = 17,500,000 kWh.
Gigacalories = 15,060 Gcal (equal to tonnes of TNT by definition).

Each point is the calculator re-run with only “Energy amount” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Energy amount	TNT equivalent (tonnes of TNT)
15.8	3,764
31.5	7,529
47.2	11,290
63	15,060
78.8	18,820
94.5	22,590
126	30,110

How to read the result

Kilotons suit events like large industrial accidents or small asteroid airbursts; megatons suit the largest nuclear tests, big volcanic eruptions and large impacts. Comparing with everyday quantities helps: 17.5 million kWh is roughly what a few thousand households use in a year, depending on the country. That comparison shows how much energy is involved, but not how it was released.

Common mistakes

Confusing short tons, long tons and metric tonnes; the energy unit is defined by 4.184 GJ regardless.
Mixing up kilotons and megatons, a factor of 1,000.
Using the food Calorie (kilocalorie) instead of the thermochemical gigacalorie.
Reading the result as a measure of damage; damage depends on distance and how energy is released.

Keep in mind: This is a unit conversion only. It does not model blast effects, damage or safety distances.

Frequently asked questions

How many joules are in a ton of TNT?

By convention, exactly 4.184 × 10⁹ J.

Why use TNT instead of joules?

It gives an intuitive scale for very large releases and is long established in reporting explosions and impacts.

Is a megaton a million tons?

Yes, 10⁶ tonnes of TNT, or 4.184 × 10¹⁵ J.

Can I convert earthquake magnitude here?

Not directly. You first need the earthquake energy in joules from a magnitude–energy relation.

Sources: NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B.8 ("ton of TNT (energy equivalent)")

Checked 9 Nov 2026. NIST Guide to the SI (SP 811), Appendix B.8, entry “ton of TNT (energy equivalent)” (factor 4.184 × 10⁹ J, as reproduced in the CRAN NISTunits documentation); conventional definition 1 t TNT = 4.184 GJ = 1 Gcal and the Hiroshima value of about 15 kt (63 TJ) as summarised in Wikipedia, “TNT equivalent”.

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