Guitar String Tension Calculator (gauge, scale length, tuning)

Understanding the guitar string tension calculator — concept and principle

This calculator works out the tension of a guitar string from its scale length, the note it is tuned to and its unit weight (or, for plain steel, its gauge). Players use it to build balanced string sets, to see how a longer scale or a lower tuning changes the feel, and to avoid overloading a neck.

Mass, length and pitch: with the default inputs the result is 16.3 lb (≈ 72.5 N for the high E).

How it is calculated

T (lb) = UW × (2 × L × F)² ÷ 386.4

UW = unit weight (mass per length) in lb per inch; L = scale length in inches; F = frequency in Hz.
For a plain steel string, UW = ρ × π × d² ÷ 4 with steel density ρ = 0.2836 lb/in³ and gauge d in inches.
Standard pitches are based on A4 = 440 Hz: f = 440 × 2^((n − 69) ÷ 12).
Newtons = lb × 4.4482216; kgf = lb × 0.45359237.

The principle

A stretched string vibrates at a frequency set by its length, tension and mass per length: F = (1 ÷ 2L) × √(T ÷ μ). Rearranging gives T = μ × (2LF)². In inch-pound units, unit weight is measured in pound-mass per inch, so dividing by 386.4 in/s², standard gravity, turns it into pound-force. Tension therefore rises with the square of the scale length and the square of the pitch: a longer scale or a higher tuning makes the same string noticeably tighter.

Worked example

Default inputs: scale length 25.5 in, E4 (1st string, 329.63 Hz), plain steel 0.010 in.

UW = 0.2836 × π × 0.010² ÷ 4 = 0.00002227 lb/in (0.398 g/m).
2 × L × F = 2 × 25.5 × 329.63 = 16,811.
T = 0.00002227 × 16,811² ÷ 386.4 = 16.3 lb.
In other units: 72.5 N, 7.39 kgf; frequency used 329.63 Hz.

Each point is the calculator re-run with only “Scale length (in)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Scale length (in)	String tension (lb)
6.38	1
12.8	4.1
19.1	9.2
25.5	16.3
31.9	25.5
38.2	36.7
51	65.2

How to read the result

Typical electric-guitar sets aim for broadly similar tensions across the strings so they feel even under the fingers; compare your figure with the other strings in the set. If you tune down, tension falls with the square of the pitch, so heavier gauges may be needed to keep the feel. The total of all six strings tells you the load on the neck.

Common mistakes

Using the gauge formula for wound strings; their unit weight must come from the maker's chart.
Entering the scale length in mm into the inch field.
Forgetting that a capo shortens the vibrating length.
Comparing tensions at different tunings without recalculating.

Keep in mind: Very high total tension can damage a neck or bridge. Follow the instrument maker's string recommendations.

Frequently asked questions

What is the tension of a .010 high E string?

About 16.3 lb (72.5 N) on a 25.5 in scale at standard pitch.

How does scale length affect tension?

Tension rises with the square of the scale length, so longer scales feel tighter.

Why divide by 386.4?

It is standard gravity in inches per second squared, converting pound-mass to pound-force.

Sources: D'Addario, "All About Guitar String Tension" · ISO 16:1975, Acoustics — Standard tuning frequency (A4 = 440 Hz)

Checked 9 Nov 2026. D’Addario, “All About Guitar String Tension” (Jan 2026): T = UW × (2 × L × F)² ÷ 386.4, UW in lb/in, L in inches, F in Hz, ×4.45 for newtons. Steel density 7.85 g/cm³ (0.2836 lb/in³) is a standard value; A4 = 440 Hz (ISO 16).

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