Guitar String Tension Calculator

String tension depends on scale length, pitch and the string's mass per length.

How the Math Works

The Guitar String Tension Calculator uses the formula T = (UW * (2 * L * f)^2) / 386.4 to determine the force required to stretch a string under vibration. Here, UW represents the string's unit weight (mass per unit length), L is the vibrating length of the string (scale length), and f is the frequency of the note in hertz. The term (2 * L * f) calculates the wave velocity, which is squared to emphasize how tension increases with frequency and length. The constant 386.4 ensures proper unit conversion, likely accounting for gravitational acceleration and metric-to-imperial transformations, resulting in tension measured in pounds-force (lbf).

Practical Applications

To use this calculator, musicians or luthiers input three key parameters: the string gauge (to determine UW), the guitar's scale length (e.g., 25.5 inches for most electric guitars), and the target note's frequency (e.g., 82.41 Hz for low E). For instance, tuning a high E string (329.63 Hz) on a 25.5-inch scale with a .010-inch gauge would require precise input of unit weight derived from manufacturer specifications. The calculated tension helps verify if the string can handle the tuning without excessive force, preventing issues like intonation errors or premature breakage.

Day-to-Day Use

This tool empowers guitarists to optimize their instrument setup and playing experience. By calculating tension, players can select appropriate string gauges for their playing style—lighter strings (lower tension) for easier bending or heavier strings (higher tension) for richer sustain and tone. It also aids in troubleshooting buzzing or sharp/flat intonation, which may stem from incorrect string tension. Additionally, luthiers use this formula to design necks and truss rods that withstand string tension, ensuring structural integrity and optimal playability for daily use.

Worked example

A low E string on a 25.5-inch scale sits around 16 lbf.

FAQ