Every magnet comparison you can find answers the same question. What does Alnico II sound like, what does Alnico V sound like, is ceramic harsh. Reasonable questions, and the answers are mostly right, and they leave out the part that will actually change your Saturday.
A pickup magnet is a force before it is a tone. It pulls on your strings. How hard it pulls decides how much room the pickup needs under them, and that number is different for every grade — which means the height that was correct for the set you took out is not necessarily correct for the set you put in.
That is the version of this comparison nobody publishes, so that is the one I want to do.
What the Grades Actually Measure
Here are the published figures for a traditional pickup bar magnet, the ones pickup winders quote when they talk about relative strength.
| Magnet | Approximate gauss | Where you find it |
|---|---|---|
| Alnico III | 470-490 | Early '54 Strats, vintage-spec neck pickups, some P-90 reissues |
| Alnico II | 530-590 | PAF-style humbuckers, "smooth" vintage single-coil sets |
| Alnico IV | 630-670 | Boutique middle ground, some Jazzmaster and P-90 sets |
| Alnico V | 710-770 | The modern default in almost everything Fender ships |
| Alnico VIII | 1200-1320 | Hot-rodded humbuckers, modern high-output |
| Ceramic | 1250-1300 | Budget pickups, and high-output metal sets |
Look at the top and bottom of that column. An Alnico III set and a ceramic set are not near neighbors that sound a little different from each other. There is roughly a two-and-a-half-to-one difference in field strength between them, and you are asking the same six strings to swing freely over both.
The Numbers Are Not a Ranking
This trips up more people than anything else in the topic, so let me be plain about it. Alnico III is weaker than Alnico II. The grade numbers describe a material recipe and, roughly, the order in which the alloys were developed — Alnico III came along after Alnico II mostly because it was cheaper to make. Higher number, weaker magnet. There is no version of the chart where the numbers climb neatly.
Alnico IV lands between II and V, which is the one place the numbering behaves itself, and it is probably why the myth survives.
Why Fender Started on Alnico III and Left
The 1954 Stratocaster — the first year, the one everybody wants — had Alnico III magnets in all three positions. Not because Leo Fender had decided that 470 gauss was the sound of the future, as far as anyone can tell, but because that is how the Telecaster pickups were already being made and there was no reason to change the process for a new model.
By 1955 the magnets were Alnico V.
That is a detail worth sitting with, because the scooped mids and tight, quick low end that everybody means when they say "Strat" is the Alnico V version of the guitar, not the first-year one. A true '54-spec set sounds drier and more mid-forward. Country before it was surf. If you have ever put a set of accurate '54 reissue pickups in a Strat and found yourself faintly disappointed that it did not do the thing you expected, that is what happened. You got the guitar. You did not get the sound, because the sound came a year later.
I have sold a number of guitars to people who were chasing a year and buying a magnet grade without knowing it.
The Table That Should Come With Every Magnet Swap
Manufacturer height specs are written for the magnet that shipped in the guitar. For a modern Fender single-coil, that is Alnico V. So the published Strat numbers — 2.4mm bass and 2.0mm treble at the neck, 2.0mm and 1.6mm at the bridge, measured from the pole piece to the bottom of the string with the last fret held down — are Alnico V numbers.
Change the magnet and the number moves. These are starting offsets from whatever chart figure applies to your guitar, not measurements. Set them, then use your ears.
| Magnet in the pickup | Starting adjustment from the chart | Why |
|---|---|---|
| Alnico III | 0.4mm closer | Weakest field of the common grades; you can buy back the output you lost with gap |
| Alnico II | 0.2mm closer | Meaningfully weaker than V, and forgiving about it |
| Alnico IV | Chart figure | Close enough to V that the published number holds |
| Alnico V | Chart figure | This is the magnet the chart was written for |
| Alnico VIII | 0.6mm further | Nearly twice the field of V; the chart number will damp your low strings |
| Ceramic | 0.6-0.8mm further | Same field range as VIII, and usually paired with a hot coil that does not need the help |
The right-hand column is the whole argument. Getting further from the strings does not cost a strong magnet much, because it started with plenty in hand. Getting closer is what a weak magnet is for.
If a note on the low E wobbles or dies early after you have set the height, the magnet pull diagnostic will tell you in five minutes whether the magnet is the cause or whether you are chasing a worn fret. The height procedure itself, including how to balance the three positions against each other, lives in the pickup position guide.
What I Expected, and What Happened
Some years back I put a set of Alnico II magnets into a humbucker-loaded guitar that had gone stiff and bright on me — the usual move, weaker magnet, softer top end, more give. I dropped them in, played it, and the guitar was transformed. Rounder. Bloomier. Everything the forums promise.
Then I measured, out of habit more than suspicion, and found I had put the pickup back about half a millimeter lower than it had been sitting, because the mounting screws had a different amount of spring tension on them and I had not paid attention.
So I reset the height to where it was before and played it again. Most of the transformation was still there — but a real slice of it, and I would say a third, was clearance. The magnet had done less than I gave it credit for and the screwdriver had done more.
The reason I bring it up is that almost every magnet swap in the world happens this way. The pickup comes out, goes back in at a slightly different height, and whatever the player hears gets filed under the magnet. It is not a small effect being mistaken for a large one. It is two effects being reported as one, and one of them was free.
Set the height back to where it was, or set it deliberately to where the new magnet wants it. Then judge the magnet.
What the Magnet Does Not Do
There is a limit to how much of your sound sits in that piece of alloy, and it is lower than the marketing implies.
Output is mostly the coil. Turns of wire and the gauge of that wire decide how loud a pickup is, by a wide margin. A ceramic magnet in a 42-gauge vintage wind is still a vintage-output pickup that happens to be brighter and to load the string harder. If you want more output, more wire is the lever, and the magnet is the trim control.
Where the magnet earns its reputation is the top end and the feel. A stronger field puts more energy into the coil per unit of string movement, which shifts where the pickup's resonant peak sits and how much the string is fighting the magnet as it decays. That is why ceramic gets called brittle and Alnico II gets called soft. Those descriptions are real, and they are also downstream of a force you can partly dial with a screwdriver.
And none of it can be fixed after the guitar. This is worth saying because it decides where you spend the evening. A magnet that is flattening your harmonics has flattened them before the signal reaches the cable, so no amp, no cab block, no impulse response and no EQ curve gets them back. That is true of a blackface Deluxe and equally true of an HX Stomp — the fault is upstream of both, and the fix is a quarter inch above the pole pieces either way.
Single-Coils Take It Worse Than Humbuckers
Geometry, not grade.
In a Strat or a Tele pickup, the pole pieces are the magnets. The alnico rods run right up to the string, and whatever the grade is, the string sees it at full strength.
In a PAF-style humbucker, one bar magnet sits underneath the coils and feeds steel slugs and screws. The steel carries the field up to the string, and it loses some on the way. Same grade, weaker field where it counts. This is a large part of why humbuckers tolerate being run close in a way single-coils do not.
P-90s land in between and get blamed for it constantly — bar magnets under the coil like a humbucker, but a single wide coil and pole screws that put a strong field right under the strings. A P-90 that sounds thick and blurry is very often just a P-90 mounted too high, which is a different complaint than the one people usually make about them under gain, covered in the P-90 overdrive guide.
Choosing, If You Are Actually Choosing
Decide by the problem you have.
Your low strings warble or die early and the height is already correct. Go weaker. Alnico II or III in a single-coil, Alnico II in a humbucker. You are buying clearance without giving up gap.
Your pickup sounds fine but the top end is glassy in a way you do not like. Alnico II is the usual answer and it will work, though try a half turn lower first, for free.
You want the '54 thing specifically. Alnico III, and be honest with yourself that it is drier and more mid-forward than the Strat sound in your head.
You play high-gain and want the front of the note to stay sharp. Ceramic or Alnico VIII, and give them the room in the table above. A tight, aggressive magnet run too close stops being tight, which is the trap.
You do not have a problem. Then leave it alone and spend the money on strings and a fret dress, which will change your guitar more than any magnet in this list.
The one thing I would not do is order a magnet grade because a forum thread described it in adjectives. Every one of those descriptions was written by somebody who also, without noticing, moved their pickup.
