TNT Equivalent Calculator
Convert any energy release into its equivalent mass of TNT, or find the TNT equivalent of a known explosive charge. Choose from 14 common explosives with pre-loaded detonation data, or enter custom heat-of-detonation values. Switch between joules, megajoules, kilotons, and more. The calculator also estimates peak blast overpressure at a given distance using the Hopkinson-Cranz scaling law and classifies the expected damage level.
Formula
Worked example
Example: 10 kg of C-4 (heat of detonation 5.734 MJ/kg). TNT factor = 5.734 / 4.184 = 1.370. TNT equivalent = 10 x 1.370 = 13.70 kg. At 50 m, scaled distance Z = 50 / 13.70^(1/3) = 50 / 2.395 = 20.9 m/kg^(1/3). Estimated peak overpressure = (0.84/20.9 + 2.7/20.9^2 + 0.65/20.9^3) x 100 = 4.08 + 0.62 + 0.007 ≈ 4.7 kPa (negligible structural damage).
What is TNT equivalent?
TNT equivalent is a standard way to express the energy of any explosion - chemical, nuclear, or mechanical - in terms of the mass of trinitrotoluene (TNT) that would release the same amount of energy. One kilogram of TNT releases exactly 4,184 kilojoules (4.184 MJ) by international convention, a figure agreed upon because real TNT batches vary by about 10 to 15 percent depending on confinement and purity. The convention makes it easy to compare events as diverse as a stick of dynamite (roughly 2 MJ) and the Tsar Bomba nuclear test (approximately 210,000,000 MJ). Scientists use tonnes, kilotonnes, and megatonnes of TNT equivalent when the numbers become very large.
TNT factor and relative effectiveness
The TNT factor (also called relative effectiveness, or RE) is the ratio of the heat of detonation of an explosive to that of TNT. An explosive with RE = 1.35, like RDX, releases 35 percent more energy per kilogram than TNT. Multiply the mass of any explosive by its RE factor to get the TNT equivalent: Weq = W_exp x RE, where RE = H_exp / H_TNT. For the reverse calculation - finding the energy of a given TNT mass - simply multiply by 4,184 kJ/kg. The same factor applies whether you want to compare demolition charges, evaluate military ordnance, or compute the energy of a non-chemical event such as a meteorite impact or an industrial accident.
Blast overpressure and damage zones
When an explosive detonates in the open, the released energy creates a rapidly expanding shock wave. The key hazard parameter is peak overpressure, the sudden rise in air pressure above ambient as the blast front passes. Engineers use the Hopkinson-Cranz (or cube-root) scaling law to relate overpressure to distance: scaled distance Z = R / W^(1/3), where R is the standoff distance in metres and W is the TNT equivalent in kilograms. The Brode (1959) empirical formula then gives overpressure in bar from Z. Even modest overpressures are hazardous: 7 kPa shatters windows, 17 kPa causes moderate structural damage, and 35 kPa is enough to collapse most residential buildings. This calculator uses the free-field (unconfined) approximation; real blast effects depend on confinement, terrain, and structural response.
Real-world reference events
Nuclear weapon yields are almost always quoted in kilotonnes (kt) or megatonnes (Mt) of TNT. The bomb dropped on Hiroshima in 1945 had a yield of about 15 kt (15,000 t TNT equivalent). The largest nuclear device ever tested, the Soviet Tsar Bomba (1961), reached approximately 50 Mt. At the smaller end, the 2020 Beirut port explosion released energy equivalent to roughly 1,000-1,500 t of TNT, enough to be detected by seismographs across the region and cause catastrophic damage within a 10 km radius. Meteorite and asteroid impacts are also measured this way: the Chelyabinsk meteor (2013) released about 440 kt, and the Tunguska event (1908) is estimated at 10 to 15 Mt.
Common explosives - heat of detonation and TNT factor
| Explosive | Heat of detonation (MJ/kg) | TNT factor (RE) | Common use |
|---|---|---|---|
| TNT | 4.184 | 1.00 | Reference standard |
| RDX / Cyclonite | 5.654 | 1.35 | Military, demolition |
| HMX / Octogen | 5.694 | 1.60 | Military, rocket propellants |
| PETN | 5.798 | 1.27 | Detonators, Semtex |
| C-4 | 5.734 | 1.37 | Military demolition |
| Semtex-H | 5.600 | 1.28 | Sheet explosive |
| ANFO | 3.097 | 0.74 | Mining, quarrying |
| Tetryl | 4.573 | 1.25 | Booster charges (legacy) |
| Nitroglycerin | 6.702 | 1.48 | Dynamite component |
| Black Powder | 2.929 | 0.55 | Propellant, fireworks |
| Dynamite 60% | 4.440 | 0.90 | Civil engineering |
| Torpex | 5.450 | 1.23 | Naval torpedoes |
| Tritonal 80/20 | 4.878 | 1.07 | Aerial bombs |
| Ammonium Picrate | 3.676 | 0.88 | Shell filler (historical) |
TNT factor (RE) = heat of detonation of explosive / heat of detonation of TNT (4.184 MJ/kg). Data from public military and engineering sources.
Frequently asked questions
What is the energy of 1 kg of TNT?
By international convention, 1 kg of TNT releases exactly 4,184 kilojoules (4.184 MJ or approximately 1,000 kilocalories). This is a defined constant, not a measured average, chosen to simplify comparisons across different explosives and events. Real TNT batches typically release between 3,600 and 4,600 kJ/kg depending on confinement and formulation.
How do I convert joules to TNT equivalent?
Divide the energy in joules by 4,184,000 (the number of joules per kilogram of TNT). For example, 41,840,000 J / 4,184,000 = 10 kg TNT equivalent. If your energy is in megajoules, divide by 4.184 to get kilograms of TNT equivalent directly.
What does the TNT factor (RE) mean?
The TNT factor, or Relative Effectiveness (RE), is the ratio of the heat of detonation of an explosive to that of TNT. RDX has RE = 1.35, meaning each kilogram of RDX releases 35% more energy than a kilogram of TNT. ANFO has RE = 0.74, so it is 26% less energetic per kilogram than TNT. Multiply the mass of any explosive by its RE to get the TNT equivalent mass.
What is Hopkinson-Cranz scaling?
Hopkinson-Cranz (or cube-root) scaling states that two charges of different TNT equivalent mass will produce the same overpressure at distances that scale with the cube root of the mass ratio. The scaled distance Z = R / W^(1/3), where R is in metres and W is in kilograms, collapses blast data from many different charge sizes onto a single curve. This lets engineers use small-scale test data to predict blast effects from much larger charges.
How is nuclear yield expressed in TNT equivalent?
Nuclear weapon yields are too large to express in kilograms, so they are quoted in kilotonnes (kt, thousands of tonnes) or megatonnes (Mt, millions of tonnes) of TNT equivalent. One kiloton = 4.184 x 10^12 joules. The Hiroshima bomb was about 15 kt, a modern strategic warhead is typically 100 to 800 kt, and the largest test ever (Tsar Bomba) reached 50 Mt.
Is this calculator suitable for professional safety and demolition engineering?
This tool is for educational and reference purposes. Professional demolition, mining, and military engineering require certified software, site-specific modelling, and compliance with national and international regulations. The overpressure estimates use a simplified empirical formula for free-field, unconfined detonations; real-world effects depend on confinement, geometry, reflected waves, and structural response.