String radius from the top or bottom of strings

A few days ago, I was asked a question related to setting string action and it occurred to me that it’s something that might be useful to a wider audience.

The question was about how we should measure and set action. If we’re measuring from the bottom of the string to the top of the fret, doesn’t that mean that the tops of the string are ‘inconsistent’ (given that each string is slightly larger than the last). Could this throw off a player when they’re picking?

It’s a good question.

Before I answer it, let me back up a little here and discuss the ways we can set action.

Should you measure string action from the top or bottom of strings?

1. Setting Action Using Maths

First, we can measure from the bottom of each string, in turn, and set each action individually. This involves some very basic maths to divide up the difference between the 1st and 6th string actions (because players generally like the 1st string lower than the 6th). The difference in heights between these two strings is ‘distributed’ evenly across the middle four strings.

So (making up metric figures for ease of demonstration) if your 1st string was 1.5mm your 6th string was 2mm, you would set your 2nd string to 1.6mm, 3rd string to 1.7, 4th to 1.8, and 5th to 1.9mm. In this way, you achieve a nice smooth and consistent change in action across the fingerboard. Nice.

Bass players: you can see how this would apply across however many strings are on your bass.

2. Setting Action Using a Radius Gauge Under the Strings

The same result can be achieved by using an under-string radius gauge. Set your 1st and 6th strings and then use the gauge under the strings while you set your middle strings.

Setting string action with under-saddle radius gauge.

Because the gauge is under the strings, you’ll end up with similar measurements as if you’d done the maths.

3. Setting Action Using a Radius Gauge Over the Strings

You can also use a regular radius gauge to set string action using the tops of the strings. Again, set the 1st and 6th strings, but this time set your middle strings with the radius gauge on top of the strings.

Setting guitar string action with radius gauge on top of strings

This is the way I recommend in my Sketchy Setups guides, mainly because it’s the easiest to explain and the easiest to do.

So what’s the difference?

Well, methods 1 and 2 set the string-to-fret distance, measuring from the bottom of the string. That’s definitively the most accurate way to do it. Method 3 aligns the tops of the strings to the fingerboard radius. That’ll be slightly less accurate (because it’s string-to-fret distance that counts).

If you set action from the bottom, the tops are not quite consistent because of string diameter. Of course, if you set from the top…

Of course, as per the question that started all of this, because each string is a different size, these first two methods will end up with the string-tops varying slightly even though the bottoms are consistent.

Method 3 gives a consistent radius along the tops of the strings so maybe it feels better to someone actually picking those strings.

But wait… That means the bottoms are inconsistent. Gaaaah!

Back to the Question

Getting back to the question that started this, will setting action while ‘keying’ from the bottoms of the strings result in inconsistency at tops of those strings?


Will that potentially affect playing feel for someone picking those strings?

Nah. I would challenge anyone to be able to tell the difference to picking feel. Weirdly (and sometimes wildly) inconsistent string saddles is a common issue I’ll fix during a setup and most players never even noticed they were out of whack.

The Bottom Line

Any of the action-setting methods above will give you perfectly good results. Measuring under the strings will be a little more accurate and measuring over the strings will be easier.

It doesn’t really matter that much though. We’re not talking major differences here. The real-world difference is tiny and I’d bet that players wouldn’t notice.

Personally, I have under-string radius gauges and I use them to set for as much accuracy as I can. If you want to get these gauges (or do the sums for calculating each string’s height) go for it. I reckon that most players setting up their own instruments can very happily download a printable radius gauge and use that on the string-tops, though. It’ll be just fine.

Radius gauges. You can download and print your own if you want.

Radius gauges. You can download and print your own if you want.

I should mention the caveat for bass (or guitars with very heavy strings). As the string size increases, the discrepancy between string top and bottom action also grows. I’d recommend measuring, or using an under-string gauge, for very heavy strings.

Otherwise, if you’re setting up your guitar, feel free to set it the way that works best for you. If this means making the tops of strings consistent, instead of the bottoms, go ahead and do that.

And I definitely wouldn’t lose sleep over it.

One last thing to just sum this up. Whether you key off the tops or the bottoms of strings, the other side will always be ‘off’. Maybe we should measure each string and subtract half its thickness from the action measurement. Then we could get the centres correct. But, when you think about it, that means the tops and bottoms are both incorrect. You can really get sucked into Pedantsville if you worry too much about this stuff so, my advice: Find something worth your worry.

This article written by Gerry Hayes and first published at