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If you’ve ever had a guitar that wouldn’t play in tune, or the action was far too high or too low, you might have been told to check the neck relief using a feeler gauge.
Neck relief, which is the amount of bow in a guitar neck, is essential to playability. But how do you measure neck relief without a feeler gauge?
If you don’t have a feeler gauge, measure neck relief by installing a capo at the first fret, then fretting the low E string by hand at the last fret. Using a precision ruler, measure the distance between the bottom of the low E string and the fretboard at the seventh fret.
Let’s look deeper at what neck relief is, why it matters, and how you can measure it, even without a set of feeler gauges.
What Is Neck Relief?
Steel strings, like most modern guitars use, put even more tension on, and can easily cause a neck to bow, which in turn can cause quite a few problems.
Too much distance between the strings and the fretboard can cause problems with intonation, while too little distance can cause strings to buzz. Too much back bow can cause both of those problems, and make the guitar less playable, too.
Until the early 20th century, if the neck of a guitar bowed, there wasn’t much you could do about it. Eventually, however, makers started putting metal bars in the necks of guitars to resist the back bow.
That evolved into the modern adjustable truss rod that’s in nearly every guitar these days.
The truss rod allows you to change the neck relief quickly. That makes your guitar more playable and prevents long-term damage to the neck from too much string tension.
It’s something every player should do a few times a year, and to do that you need to do some work.
How Do You Measure Neck Relief?
In order to know how much to adjust the truss rod, you need to start out by measuring the neck relief.
The standard way to measure it is to hold the guitar like you’re going to play it and put a capo at the first fret. With your playing hand, hold down the low E string at the fret closest to the body, and use a feeler gauge to measure the distance between the bottom of the string and the top of the seventh or eighth fret.
The normal relief for an electric guitar is between .005” and .020”.
If your measurements come out outside that range, then it’s time to adjust the truss rod. Different makers install them differently, but this video gives a good overview of how to use the truss rod to adjust the neck relief.
How Do You Measure Neck Relief With A Straight Edge?
Not everyone has access to a feeler gauge set, however. You can get a precise measurement with a tool many people do have access to, however, a ruler with markings for thousandths of an inch.
To use a ruler, you set up the measurement in a slightly different way than with a feeler gauge. Instead of holding the guitar like you were about to play, set it down and make sure the neck is well supported.
Put a capo at the first fret, then fret the low E string on the last fret. Use the ruler to measure the distance between the bottom of the string and the top of the seventh or eighth fret.
This only works if you have access to a fairly precise kind of ruler, but engineer rulers are quite common, so many people have access to that kind of precision.
What if you don’t have feeler gauges, a precision ruler, or any special tools at all? Even then there are still plenty of things you can use to measure the neck relief. You just need to get a little bit creative.
How To Measure Neck Relief Without Special Tools
If you don’t have a ruler that measures in thousandths of an inch or a set of feeler gauges, that doesn’t mean you can’t check your neck relief.
Instead of using measuring or marked items, though, you have to have some sense of what you’re going to use to measure. Let’s look at some common options and how you can use them.
Paper: This might seem silly, but it can work quite well. Paper stock is measured in a few different ways, from points to mil, but all of them are just about equivalent to .001”.
Most printer paper is between .009” and .011” thick, while business cards can range from .014” to .016.”
To measure neck relief, you can use paper of a known thickness and add more sheets if the distance is larger than just one sheet. In addition, other stiff items like guitar picks, can work to measure the relief, as long as you know the thickness in advance.
Guitar strings: You can do this a few different ways. This video shows how you can use the diameter of the B string to check relief.
There are more accurate methods, though, and ones that can get your relief closer to exact.
Like paper, strings are different thicknesses, but in the case of strings, they’re much easier to tell, and they come in packs with multiple thicknesses.
The high E string on a set of light gauge acoustic guitar strings is usually .011”, for example, while other strings are between .015” and .030”.
That means one set of strings can give you a pretty decent idea of where your neck relief is.
To use strings or paper, follow the same basic procedure as for the feeler gauges. Hold the guitar like you’re getting ready to play it, and put a capo on at the first fret.
Hold down the low E string at the fret closest to the body and slide the string you’re using between the top of the seventh fret and the bottom of the string.
If the string slides in smoothly, then go up to a larger size, while if it hits the string or the fret, go down to a thinner diameter.
While using a feeler gauge or another specialty item to measure neck relief will be the easiest and most accurate method, not everyone has the tools they need to make that happen.
But that doesn’t make neck relief any less important. After all, it can affect action height, intonation, fret buzz, and a lot more.
So don’t be afraid to use the tools or items you already have around the house to make sure your guitar is playing as well as it can be.
I’ve been a musician, particularly a guitarist, for more than 25 years. I love writing about guitars, gear, recording, music in general and more.