Guitar action height and neck relief
Action is the gap between the top of the fret and the underside of the string. It depends on neck relief (set with the truss rod), saddle height and how deep the nut slots are cut. Pick the instrument and the page shows the figures the maker publishes, with the fret they're measured at and the source.
Reference string action
Low and high string height, neck relief and the measuring fret, as each maker publishes them for its lines.
| Instrument | Low (mm) | High (mm) | Relief (mm) | Fret |
|---|---|---|---|---|
| Fender electric | 1.6 | 1.6 | 0.3 | 17 |
| PRS electric | 1.5–1.9 | 1.4–1.8 | 0.1–0.3 | 12 |
| Martin acoustic | 2.0–2.3 | 1.4–1.7 | 0.1–0.1 | 12 |
| Classical guitar | 4.0 | 3.2 | 0.1 | 12 |
| Fender bass | 2.4 | 2.0 | 0.3 | 17 |
| Ukulele | 3.0 | 3.0 | – | 12 |
| Mandolin | 1.9 | 1.7 | 0.1 | 12 |
| Banjo | 3.2 | 3.2 | 0.4–0.5 | 22 |
How to use it
- With the instrument in tune, start with relief: hold the string down at the frets listed under Reference values and measure the gap at the 8th fret with feeler gauges.
- If the gap is off, turn the truss rod in small fractions of a turn and let the wood settle before you measure again.
- Measure the low and high strings at the listed fret and enter them under Measured now. The target starts at the middle of the reference range.
- Raise or lower the saddle by the amount shown, retune and measure again.
Help and explanations
Enter what you measured and what you want: the calculator tells you how far to raise or lower the saddle on each side. An on-screen ruler, calibrated with a credit card, helps when you don't have a string action gauge.
The saddle rule
The string is a straight line from nut to saddle. When the saddle drops, action falls in proportion to the distance from the nut: at the 12th fret, halfway along the scale, action changes by half of what the saddle moved. To lower action at the 12th by 1/64″ (0.4 mm), take 1/32″ (0.8 mm) off the saddle. At the 17th fret, where Fender measures, the ratio is 1.6 to 1. On an acoustic, sand the bottom of the saddle a little at a time: go too low and you need a shim or a new saddle.
Neck relief and the truss rod
A slight forward bow lets the string vibrate without hitting the middle frets. The truss rod works against string tension: tightening it reduces relief, loosening it adds relief.
American makers publish setups in 64ths of an inch (1/64″ = 0.397 mm). Fender lists 4/64″ (1.59 mm) on both outer strings at the 17th fret for 9.5″ to 12″ radius necks; Gibson measures at the 12th.
Tips
- Change one thing at a time: truss rod, saddle, nut. Retune after each adjustment.
- Changed the action? Intonation changes with it: check it with the intonation checker.
- New gauge or tuning? Relief changes too; see the difference in the string tension calculator.
Frequently asked questions
What is a good action height for an electric guitar?
For 9.5″ to 12″ radius necks, Fender lists 4/64″ (1.59 mm) on the low and high E at the 17th fret. Other makers are in the table, each at the fret they measure.
How much should I lower the saddle?
Twice what you want to remove at the 12th fret: to go from 2.4 to 2.0 mm (about 6/64″ to 5/64″), lower it 0.8 mm (1/32″). If you measure at the 17th, multiply the difference by 1.6.
How do I adjust neck relief with the truss rod?
Measure the gap at the 8th fret. More than the reference: tighten the rod; string touching the first frets: loosen it. Turn no more than 1/4 turn at a time and measure again.
What is the action height on an acoustic guitar?
On steel-string acoustics it's measured at the 12th fret; Martin's and Taylor's figures are in the table, with the source. Classical guitars run higher, because nylon swings wider.
How much is 1/64 of an inch?
0.397 mm. So 3/64″ = 1.19 mm, 4/64″ = 1.59 mm, 5/64″ = 1.98 mm and 6/64″ = 2.38 mm.
Can I measure action with my phone?
Yes, with the on-screen ruler calibrated by a credit card (85.60 mm, 3.370″, ISO/IEC 7810). Rest the edge of the screen on the fret and compare the string with the 1 to 4 mm steps.