Earthquake Magnitude Scale Table
| Magnitude | Class | Typical effects | Energy vs M 5 |
|---|---|---|---|
| under 2 | Micro | not felt, logged daily by networks | tiny |
| 2-3.9 | Minor | felt by a few indoors | 1/31,623 |
| 4-4.9 | Light | windows rattle, lamps sway | 1/31.6 |
| 5-5.9 | Moderate | dishes break, plaster cracks | 1 |
| 6-6.9 | Strong | chimneys crack, furniture moves | 31.6 |
| 7-7.9 | Major | well-built structures damaged | 1,000 |
| 8 and up | Great | bridges and foundations destroyed | 31,623 |
Magnitude is the size of an earthquake at its source - the seismic moment released by the fault - and the scale is logarithmic twice over: each whole step up multiplies the recorded ground motion by about ten and the energy released by about 31.6. Type a magnitude and the converter names its class, describes typical shaking, and prices its energy against a magnitude 5 reference quake.
The classes in the table are the convention seismologists and agencies report by: minor quakes rattle windows, moderate quakes crack plaster, strong ones damage chimneys, and the great quakes above magnitude 8 release more energy in a minute than a city uses in years. The numbers are instrument readings, not damage scores - a magnitude 6 under the ocean can pass unnoticed while the same quake under a city is a disaster, which is why agencies also publish intensity scales that grade effects place by place.
How to use
- Type a magnitude - the class, a plain-language effects line and the energy multiple versus magnitude 5 appear instantly.
- Read the energy column in steps, not linearly: 6 is 32 times a 5, 7 is a thousand times, 8 is about thirty-two thousand times.
- Pair magnitude with depth and distance: shallow quakes shake harder at the surface, and the same magnitude 100 miles away may only sway lamps.
Frequently asked questions
What is the difference between magnitude and intensity?
Magnitude is one number for the whole earthquake - the energy released at the source. Intensity is a place-by-place grade of what people felt and what broke, written with Roman numerals from I to X in the Modified Mercalli scale. The same magnitude 6 quake produces intensities of VIII near the fault and II two hundred miles away; news reports quote magnitude, damage surveys quote intensity.
Is the Richter scale still used?
The name survives in conversation, but modern agencies report moment magnitude (Mw) instead. Charles Richter's 1935 scale was calibrated on Southern California seismographs and saturates - it underestimates very large quakes - while moment magnitude keeps measuring accurately up the range and matches the old numbers for small and moderate events. The USGS now lists all magnitudes as M with the moment magnitude preferred.
How much more energy is a magnitude 7 than a 6?
About 31.6 times - one full step multiplies energy by 10 to the 1.5. Two steps (5 to 7) is a thousand-fold, three steps about 31,600-fold. Ground motion grows by roughly ten times per step, which is a separate figure often quoted; energy is the cube of that, and the gap is why magnitude 7 is a catastrophe while magnitude 6 is a serious earthquake.
How many earthquakes happen every year?
Millions are recorded, most too small or too remote to feel. Agencies estimate roughly ten thousand to fifteen thousand quakes a year in the magnitude 4-to-5 band, about thirteen hundred to fifteen hundred at magnitude 5-to-6, and one hundred thirty to one hundred sixty at 6-to-7; great quakes of magnitude 8 and above arrive roughly once a year somewhere on the planet.
What magnitude is dangerous?
Damage begins around magnitude 5 where buildings are vulnerable and becomes likely near 6, which is why the class ladder calls 5-to-5.9 moderate and 6-to-6.9 strong. Depth and construction dominate the outcome: a shallow 6 under unreinforced masonry is far deadlier than a deep 7, and the deadliest quakes in history were magnitude 7-to-9 events under dense cities.