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magnitude

/ˈmæɡnɪtuːd/·noun

the size or scale of something — often as a measured value on a scale
Fig. 1 — The first tremor barely troubles the house: the stylus stitches a small wiggle onto the scrolling drum, and the readout says M 2.4.
01Definition

Magnitude is how big a thing is — in the loose sense of scale and importance ('the magnitude of the challenge') and in the strict sense of a measured value: the magnitude of an earthquake, of a star's brightness, of a vector. From Latin magnitudo, from magnus, 'great'. Science leans on it precisely because it separates size from every other property: two quakes can strike the same fault and differ only in magnitude — the amount of energy released — which is exactly what instruments exist to quantify. The threshold between a tremor you sleep through and one you remember is a couple of numbers on that scale.

02In use
  • iOnly after the flood did the town grasp the magnitude of what it had lost.
  • iiThe 1960 Chilean quake still holds the largest magnitude ever recorded.
  • iiiTheir estimate was off by an order of magnitude — ten times too small.
03Collocations
  • the magnitude of the problem
  • an order of magnitude
  • a magnitude 7 earthquake
  • sheer magnitude
  • underestimate the magnitude

Family magnitudes (plural noun) · magnify (verb) · magnificent (adjective)

04Relations

=size, scale, extent, enormity, intensity

≠insignificance, smallness

06TOEFL & IELTS

Own the phrase 'an order of magnitude': it means a factor of ten, so 'an order of magnitude larger' is roughly ten times bigger and 'two orders' a hundred — a precision tool for data essays that most candidates never deploy. 'The magnitude of the problem/task/loss' is the essay collocation for scale with gravity. In science passages the measured sense rules: earthquake magnitude (energy at the source, logarithmic scale) and stellar magnitude (brightness — counterintuitively, lower numbers mean brighter). Stress up front: MAG-ni-tude.

07Asked
What does magnitude mean?
The size of a thing — either loosely (the magnitude of a crisis: its sheer scale and seriousness) or as a measured value on a scale. The scene above stages the measured kind: two earthquakes hit the same house through the same instrument, and everything about them is identical except the number on the drum — 2.4, then 6.1. Magnitude is that number: not what happened, but how much of it.
What does 'order of magnitude' mean?
A factor of ten. Something an order of magnitude bigger is roughly ten times bigger; three orders of magnitude is a thousandfold. The phrase is precision equipment for talking about very unequal quantities — 'the two estimates differ by two orders of magnitude' tells you one is about a hundred times the other — and 'the same order of magnitude' means within a factor of ten: comparable, as scientists count comparable.
What is the difference between an earthquake's magnitude and its intensity?
Magnitude measures the event at its source — the energy released, one number per quake, read from instruments; the scale is logarithmic, each whole step releasing about thirty-two times more energy. Intensity measures the shaking felt at a particular place, so a single quake has one magnitude but many intensities, strongest near the epicentre. News reports blur them; geology passages test the difference.
What does magnitude mean for a vector or a force?
Its size stripped of its direction. A vector is an arrow with both; its magnitude is just the arrow's length — always zero or positive, never negative. So 'the magnitude of the force is 20 newtons' reports how hard, saying nothing about which way. Physics English uses the word constantly for exactly this separation, and it is the same how-much idea the earthquake scale applies to energy.
What is the difference between magnitude and amplitude?
Amplitude is a wave's height — how far the ground, or the signal, swings from rest; it is what a seismograph pen literally draws. Magnitude is computed from amplitude after correcting for distance and instrument, producing one number for the whole event. So amplitude belongs to the recording at a given place, magnitude to the earthquake itself — a derived summary, not a raw measurement.
Why do brighter stars have lower magnitudes?
Because the scale is a ranking, not a measurement: the ancient Greeks sorted visible stars into six classes with the brightest called 'first magnitude', and astronomy kept the order when it made the scale numeric. So the numbers run backwards to intuition — Sirius sits at about −1.5, the faintest naked-eye stars near +6. The word still means size; here it is the size of the rank.