The Earthquake Magnitude Scale Explained
By Quake Tracker Live Editorial · Published November 9, 2026
When an earthquake makes the news, the first number you hear is its magnitude. It is a single figure that tries to describe how much energy the fault released, and it is the number you will see next to every event on our live earthquake map. But magnitude is easy to misread. A magnitude 7 is not "a bit more" than a magnitude 6, and the "Richter scale" that most people still mention is no longer what scientists use for large events. This guide explains what the number really means.
What magnitude measures
Magnitude is a measure of the size of the earthquake at its source. It does not depend on where you are standing. One earthquake has one magnitude (although agencies may disagree by a tenth or two while they refine their analysis), but it produces very different shaking in different places. How strongly the ground shakes where you are is called intensity, and it depends on your distance from the fault, the depth of the quake, the local soil and the type of building you are in.
The scale is logarithmic. For the common magnitude scales, each whole-number step up means:
- about 10 times larger ground motion recorded on a seismogram, and
- about 32 times more energy released (the exact factor is roughly 31.6).
That is why a magnitude 8 releases around a thousand times more energy than a magnitude 6, not just "two more".
Logarithmic scale: each gridline is 10 times the previous one.
View the data
| Magnitude | Energy (M5 = 1) |
|---|---|
| Magnitude 5 | 1× |
| Magnitude 6 | about 32× |
| Magnitude 7 | about 1,000× |
| Magnitude 8 | about 32,000× |
| Magnitude 9 | about 1,000,000× |
Each whole step multiplies the energy by about 32 (10 to the power 1.5). A magnitude 9 releases about a million times the energy of a magnitude 5.
The Richter scale: where it came from
Seismologist Charles Richter developed the first widely used magnitude scale in 1935 at the California Institute of Technology, working with Beno Gutenberg. It was designed for a specific job: ranking earthquakes in Southern California recorded by a particular type of instrument, the Wood-Anderson seismograph. Richter took the largest swing of the seismograph needle, corrected it for the distance to the epicenter, and put the result on a base-10 logarithmic scale. The result is now called local magnitude (written ML).
The Richter scale worked well for moderate, nearby, shallow quakes. It had limits, though:
- It was calibrated for Southern California rock and one instrument type.
- It saturates for large events: above roughly magnitude 7, the measured amplitude stops growing in step with the true size of the quake, so a giant earthquake and a very large one can look similar.
- It is not a good fit for distant earthquakes recorded far from the source.
Moment magnitude: what scientists use today
In 1979 Thomas Hanks and Hiroo Kanamori proposed moment magnitude (written Mw). Instead of the height of a needle swing, it is based on the seismic moment, a physical quantity built from three things: how stiff the rock is, how large the fault area that slipped was, and how far the fault slid on average. It does not saturate, it works for any distance, and it can be calculated from long-period waves that reveal the whole rupture. For this reason the U.S. Geological Survey (USGS) and agencies worldwide report moment magnitude for most significant earthquakes.
You will see a few variants in the catalogs, and we show the type on each earthquake page when it is available:
| Label | Name | Typical use |
|---|---|---|
| ML | Local magnitude (Richter) | Small and moderate nearby quakes |
| mb | Body-wave magnitude | Quick global estimates, mid-size quakes |
| Ms | Surface-wave magnitude | Shallow quakes in the M5 to M8 range |
| Mw, Mww, Mwc, Mwr | Moment magnitude (computed from different wave data) | Significant earthquakes worldwide |
Moment magnitude variants differ in which waveforms and methods were used. For a given earthquake they usually agree within a tenth or so.
The scales are tuned to agree with each other in the ranges where they overlap, which is why a "magnitude 6" means roughly the same thing no matter which one produced it. The "Richter scale" survives mostly as a popular name.
What each magnitude level feels like
The table below follows the descriptive classes used by the USGS, together with the typical effects the agency associates with each range. Real-world effects vary widely. A deep or offshore magnitude 6.5 may cause little damage, while a shallow magnitude 6 under a city can be destructive (see our guide to earthquake depth).
| Magnitude | Class | Typical effects | Roughly how often worldwide |
|---|---|---|---|
| Below 3 | Micro / very minor | Rarely felt by people, recorded by instruments | More than a million per year (estimated) |
| 3.0 to 3.9 | Minor | Often felt indoors, hanging objects swing, rarely any damage | Around 130,000 per year (estimated) |
| 4.0 to 4.9 | Light | Felt by most people nearby, rattling windows and dishes, minor damage is unusual | Around 13,000 per year (estimated) |
| 5.0 to 5.9 | Moderate | Felt widely, can damage poorly built structures near the epicenter | About 1,300 per year |
| 6.0 to 6.9 | Strong | Can be destructive within tens of kilometers, especially in populated areas | About 130 per year |
| 7.0 to 7.9 | Major | Serious damage over large areas | About 15 per year |
| 8.0 and above | Great | Can destroy communities near the epicenter and trigger ocean-wide tsunamis | About 1 per year |
Frequencies are the long-term annual averages published by the USGS; the smallest classes are estimates because many tiny quakes in remote areas are never recorded.
Logarithmic scale: each gridline is 10 times the previous one.
View the data
| Magnitude | Earthquakes per year |
|---|---|
| M3.0 to 3.9 | about 130,000 |
| M4.0 to 4.9 | about 13,000 |
| M5.0 to 5.9 | about 1,300 |
| M6.0 to 6.9 | about 130 |
| M7.0 to 7.9 | about 15 |
| M8.0 and above | about 1 |
Long-term annual averages published by the USGS. Each step down in magnitude brings roughly ten times as many earthquakes.
Magnitude versus intensity
Intensity describes what happened at a particular place. The scale most often used in the United States is the Modified Mercalli Intensity scale, which runs from I (not felt) to XII (near-total destruction) and is based on observed effects: whether people noticed, whether objects fell, whether buildings cracked. The USGS collects thousands of reports through its "Did You Feel It?" system and turns them into shaking maps.
A useful way to remember the difference: magnitude is like the wattage of a light bulb, and intensity is how bright the light looks from where you are standing. The same bulb looks brighter close up, dimmer far away, and different through frosted glass.
Why the number changes after the first report
If you watch a major earthquake unfold, you will often see the magnitude revised in the first minutes and hours. Automatic systems publish a first estimate within minutes, using whichever quick method is available. Analysts then recompute the event using more stations and better methods, and the magnitude type may change, for example from mb to Mw. For very large events, the first estimate can be off by a few tenths because the rupture is still going on while the first waves are being measured. The same goes for depth and location, which is why we flag preliminary solutions on individual earthquake pages.
Real examples across the scale
- M6.9, Loma Prieta, California (1989): shallow, strong shaking across the San Francisco Bay Area, famous for interrupting a World Series game.
- M6.7, Northridge, California (1994): a hidden thrust fault under Los Angeles produced damaging shaking.
- M7.1, Ridgecrest, California (2019): the strongest earthquake in California in about twenty years, in a sparsely populated desert area. A M6.4 foreshock happened about a day and a half earlier.
- M9.2, Prince William Sound, Alaska (1964): the largest earthquake in U.S. history. See our list of the largest earthquakes in U.S. history.
How to use magnitude in practice
- Treat magnitude as a size indicator, not a damage forecast. Check depth, distance to people and local reports as well.
- Remember the logarithm: add one unit and think "about 30 times the energy", not "a bit more".
- Expect revisions: a first number is a first number. Look for the type (Mw is the most reliable for large events).
- Use the today page and the biggest quakes list to see current events sorted by size.
Frequently asked questions
Is the Richter scale still used?
Mostly as a popular name. Scientists and agencies such as the USGS report moment magnitude (Mw) for significant earthquakes because it does not saturate for large events. Local magnitude (ML), the original Richter calculation, is still used for many small regional earthquakes.
How much stronger is a magnitude 7 than a magnitude 6?
The recorded ground motion is about 10 times larger and the energy released is about 32 times greater. Two steps (for example M8 versus M6) means roughly 1,000 times more energy.
Can an earthquake have a negative magnitude?
Yes. The scale has no lower limit, and very small events recorded by sensitive instruments can have magnitudes below zero. They are far too small to be felt.
Why do two websites show different magnitudes for the same earthquake?
Agencies use different stations, methods and magnitude types, and each updates its estimate as more data arrive. Differences of a tenth or two are normal, and early values are often revised. Check the magnitude type and the source on the earthquake page.
What is the largest possible earthquake?
There is no fixed upper limit on the scale, but magnitude is tied to the size of the fault that can rupture. The largest earthquake ever recorded instrumentally is the 1960 Chile event at M9.5. See our guide to the largest earthquakes in the world.
Sources and further reading
- USGS: Magnitude types
- USGS: Earthquake magnitude, energy release and shaking intensity
- USGS: The Modified Mercalli Intensity scale
This guide is general information, not professional or emergency advice. Quake Tracker Live is not an official warning system; follow instructions from local authorities.