What size frets does this guitar have? What size frets do I want? The best way to know that is to play a lot of different guitars and note/measure the sizes.
Fretsizes can be confusing. They are small measurements but have a big impact on feel and the size designations can vary. Its best in my opinion to think and talk of frets in their actual crown widths and heights rather than the old Dunlop numbers (the originator of the 6xxx numbering system) as they can mean different things to different people; i.e. Warmoth lists 6105 as .095-.047" while USACG has is at .090-.055" - these are two very different feeling fretsizes.
Fretwire can vary from some makers as it is shaped by extrusion thru a series of roller dies and the dies wear. I have observed actual Dunlop 6105 in my shop varying from .088” to .090” wide and from .052” to .055” tall. Due to the inconsistent size and tang formation, I generally do not use Dunlop fretwire these days, instead preferring the more accurate German made Jescar or the Japanese made Stewart McDonald fretwires. Both Jescar and SM have very well formed tangs and barbs and are very consistent. I will refer to the Dunlop numbers below but only for very general description – always verify actual sizes!
Guitar frets can vary from .070" (narrow, mandolins are narrower) to .115" (Ibanez JEMs and Dunlop 6000) wide and ~.02x" (really worn, fretless wonder etc) to .057" (Jescar FW11057 or fretwire that is not seated well).
"Vintage" fretwire is most usually known as "medium" fretwire and that size in today's measurements is usually .080-.040"; what you would see commonly on a Fender RI or Martin acoustic. I mention this as fretwire does vary and some "vintage" wire back in the day on the guitars was as narrow as .070". It is commonly referred to in Dunlop numbers as 6230.
Narrow fretwire encompasses the vintage/medium sizes and ranges from .070 to .095” wide. There are tall/narrow sizes available – SM 155 at .080-.050” and FW09055 (6105) at .090-.055”
Medium Jumbo in old school parlance usually indicates ~.100-.104” width and .040-.048” height and first appeared in 1959 on Gibson guitars (some say late 1958). Medium refers to height and jumbo to the width. PRS uses a medium jumbo size exclusively (except for the US made Santana models, which use a slightly bigger size).
Jumbo fretwire is the really big stuff like Dunlop 6100 and equivalent sizes at ~.110-.055” or Dunlop 6000 (Ibanez JEM series).
Electric basses tend to use a medium jumbo fret as most Fenders have thru the years. There are some folks who like the medium or even the very narrow/small mandolin fretwire for basses – this is more of a vintage feel, like the earliest Fender basses (Fender created the Precision Bass in 1951). Since string height for bass strings is higher due to gauge and tuning, they are easy to grip and many bassists do not seem as concerned about fret height as guitarists.
Please see here for available fret sizes:
If you want to measure the fret size on existing instruments, a good way to do it is to get an inexpensive dial caliper (think Harbor Freight etc). You can measure the width with the outer jaws (make sure to zero out the calipers for accurate measurements), but for the height (unless you are going to notch the depth rod and subtract the difference), use a piece of something of a uniform thickness and drill a hole in it to accomodate the depth rod, place it across two frets and measure thru the hole (usually near the crown) to the fingerboard and subtract your piece's thickness. When measuring fret height, it is always good to measure a few different places on the neck as the height may vary according to leveling and wear. On many guitars (but not all) the upper frets (if there is not a neck joint area hump that was accounting for during leveling) will be a good indicator of fret height.
Frets on finished fingerboards may be tough to measure accurately when the finish has appreciable thickness (think Rickenbackers, 70s Fenders) as these manufacturers spray the finish over the fretted neck. I have measured a finish chip from a 70s Fender maple neck refret that was .010” thick – lowering the fret height by .010” (25% in the case of the stock medium wire at the time) from just finish alone. I recently refretted a 2008 Fender Eric Johnson Strat where the fret height prior to any work was .040”, yet the crown of the fret removed from the fingerboard was .045”. I personally do not like this feel and so often I will suggest refretting over a finished fingerboard when working with them rather than under the finish.
If you cannot find an exact size you prefer, you could select a size with the width you want, but taller height and level then down to where you want them. There are times (usually during partial refrets) where I have altered the width of a fret to suit; this adds extra time to the prep work and so I charge accordingly.
There is no real rule on what fretsize is best – it is purely personal preference. To find out what size is right for you or for a specific guitar and application, you may have to try similar guitars with different fretsizes. I have heard many differing opinions on fretsize over the years; some say tall wire is too bumpy for sliding into position or that tall wire causes them to play sharp (from overly pressing down the strings, these players are used to feeling fingerboard surface under their finger tips). Some say that fretwire below a certain height is difficult to bend on. Bending and fretting hand slurring techniques are easier when the string can be addressed towards the middle of the ball end of the fingertip so that it may be pushed and pulled from the side rather than fretted from directly on top by the lower part of the fingertip. Some folks like a low fretwire as it feels very smooth to them and they don’t do a lot of slurring techniques.
Editorial comment – I advise folks when considering fretwork to consider not choosing a size or leveling operation resulting in less than .040” height if they want to play a style with frequent fret hand slurring, i.e. rock, blues, shred etc. Low fret height is less capable of sustaining a reasonable fret leveling in the future, making it that much closer to refret time. You don’t have to choose a very tall size if that is uncomfortable for you, but only choose a low height if that is really what you want and are accustomed to.
My personal favorites are the .090-.055” size for most electric guitar applications followed by the .100-.050” for more of what I think of as a Gibson/PRS/modern jazz blues guitar fret – both sizes are great for bending. I like the classic medium .080-.040” for acoustics.
The #1 cause of fret wear is the fretting hand pressure exerted by the player. I have some clients that grip very tightly and wear frets quickly (Rob Fahey), and some that grip very lightly and take forever to exhibit significant wear (Jasan Stepp, Dog Fashion Disco/PolkaDot Cadaver). Fret material hardness, string hardness and frequency of use all contribute to wear as well, but hand pressure is still the leading cause since frets do not wear themselves out. Technique is different for every player, unique and personal and habits can be hard to change. Just like brakes in a car, how hard and how much something is driven directly impacts wear and longevity. Please see the refrets page for further thoughts on this topic.