Seismic Energy Calculator
Calculate earthquake energy in joules from magnitude (Mw).
See TNT equivalent, Hiroshima bomb equivalents, and comparison to historical earthquakes.
Earthquake energy measurement has a fascinating history. Charles Richter developed the local magnitude scale (ML) in 1935 as a quick field tool for comparing earthquakes in Southern California. It was never intended to be a global, physically rigorous scale. In 1977, Hiroo Kanamori developed the Moment Magnitude scale (Mw), which is tied directly to the physical energy released: the area of the fault rupture, the amount of slip, and the rigidity of the rock. Mw is what seismologists use today for large earthquakes.
The Gutenberg-Richter Energy Formula: log₁₀(E) = 1.5 × Mw + 4.8
Where E is energy in joules. This formula was developed by Beno Gutenberg and Charles Richter in the 1950s from empirical seismograph data. Rearranged: E = 10^(1.5 × Mw + 4.8)
The 31.6× Rule: Each whole-number increase in magnitude = 31.6× more energy (because 10^1.5 = 31.62). Each whole-number increase = 10× more amplitude on a seismograph, which is why people confuse the two. Energy and amplitude scale very differently.
Magnitude to Energy Reference Table:
Every row here is the formula above, worked out. Nothing is rounded to make a story.
| Magnitude | Energy (Joules) | TNT Equivalent | Real Example |
|---|---|---|---|
| 2.0 | 6.3 × 10⁷ J | 15 kg | Barely felt, mining blast |
| 4.0 | 6.3 × 10¹⁰ J | 15 tonnes | Minor damage near epicenter |
| 5.0 | 2.0 × 10¹² J | 480 tonnes | Felt widely, light damage |
| 6.0 | 6.3 × 10¹³ J | 15 kilotons | Hiroshima bomb equivalent |
| 7.0 | 2.0 × 10¹⁵ J | 480 kilotons | Major, 2010 Haiti |
| 8.0 | 6.3 × 10¹⁶ J | 15 megatons | Great, 1906 San Francisco (M7.9) |
| 9.0 | 2.0 × 10¹⁸ J | 480 megatons | 2011 Tōhoku, Japan (M9.1) |
| 9.5 | 1.1 × 10¹⁹ J | 2.7 gigatons | 1960 Valdivia, largest ever recorded |
The Hiroshima row is the one people misremember. A magnitude 6 earthquake, not a magnitude 5, is the one that matches the 1945 bomb. The 1994 Northridge quake (M6.7) released roughly ten Hiroshimas and did $20 billion of damage in a single county.
Richter Scale vs Moment Magnitude: The original Richter scale (ML) is a logarithmic measure of seismograph amplitude corrected for distance and instrument response. It saturates above about magnitude 7, so large earthquakes all appear similar on the scale even when they differ enormously in energy. Mw does not saturate and remains physically meaningful for the largest events.
The 2011 Tōhoku Earthquake (Mw 9.1): Energy released: ~2.8 × 10¹⁸ joules, about 670 megatons of TNT. That is roughly 45,000 Hiroshima bombs. The earthquake shifted the Earth’s axis by about 17 cm and shortened the day by 1.8 microseconds. The resulting tsunami killed nearly 20,000 people and caused the Fukushima Daiichi nuclear disaster.
1960 Valdivia, Chile (Mw 9.5, Largest Ever Recorded): Energy ≈ 1.1 × 10¹⁹ J, near 2.7 gigatons of TNT. It accounted for roughly a quarter of all the seismic moment released worldwide during the entire 20th century.
You will find far larger numbers than that quoted for Valdivia, some as high as 180 gigatons. They are not typos. The Gutenberg-Richter formula gives the energy radiated as seismic waves, which is only a small slice of the total work the rupture did; most of it went into friction and heat on the fault plane and never travelled anywhere. Both figures are defensible answers to different questions. Everything on this page uses the radiated-energy figure, because that is what the formula computes and what the magnitude scale is built on.
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This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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