Earthquake Calculator

M_w	Class	kt TNT
< 3.0	Micro / Minor	< 0.015
3.0 – 3.9	Minor	0.5
4.0 – 4.9	Light	15
5.0 – 5.9	Moderate	476
6.0 – 6.9	Strong	15,000
7.0 – 7.9	Major	476,000
8.0 +	Great	≥ 15 Mt

Earthquake calculator

With this earthquake calculator, you can estimate the energy release of an earthquake from its moment magnitude. Because enormous energy values expressed in joules are not very intuitive, we also translate the result into more familiar equivalents — tons of TNT, kilotons, megatons, and the number of Hiroshima-scale atomic bombs 💣. The tool is also a safe bet when you want to compare two earthquakes and find out how much stronger one is than another.

Below you'll learn about the different measures of an earthquake: from the famous Richter scale to the currently used moment magnitude scale and the Mercalli intensity scale.

Richter scale

Let's start with a disclaimer that for some may be obvious: the Richter scale is not widely used anymore, but it still happens to be mentioned erroneously in the news from time to time.

The Richter magnitude is based on the wave amplitude recorded by seismographs. Charles Richter developed this logarithmic scale in 1935 to compare local earthquakes — the ones in southern California with an epicenter up to 370 miles (600 km) from the seismograph. Because the scale was intended for a specific area only, and seismographs of that period weren't as sensitive as today's, large earthquakes were systematically underestimated. The key point to remember: on the Richter scale, wave amplitudes are taken into account.

Moment magnitude scale

When you hear about an earthquake in the news, the measure given is the magnitude — the moment magnitude (M_w), to be exact. It is the most reliable way of presenting the relative size of an earthquake, especially for large events. The strongest earthquake ever recorded — Chile in 1960 — was 8.6 on the Richter magnitude scale but had a moment magnitude of about 9.5.

To find the moment magnitude, seismologists first determine the seismic moment, M₀, and then convert it (Hanks & Kanamori, 1979):

M_w = (2/3) · (log₁₀ M₀ − 9.1)     (M₀ in N·m)

Rearranged, this gives the seismic moment used by our calculator:

M₀ = 10^(1.5 · M_w + 9.1) N·m

The radiated seismic energy is estimated from the Gutenberg–Richter energy–magnitude relation:

log₁₀(E) = 1.5 · M + 4.8     (E in joules)

Because the scale is logarithmic, every 1.0 step up in magnitude releases about 31.6× more energy, while ground shaking (amplitude) grows about 10× per step. Two whole steps up therefore mean roughly 1000× more energy.

Modified Mercalli intensity scale

Unlike magnitude, which measures the size of the earthquake at its source, the Modified Mercalli Intensity (MMI) scale describes the effects of shaking at a given place — from I (not felt) to XII (total destruction). Intensity depends on distance from the epicenter, depth, and local geology, so a single earthquake produces many different intensity readings. Our calculator focuses on magnitude and energy; the class column gives a rough guide to how such an earthquake is usually felt near the epicenter.