What formula is used to calculate string tension?

Tension equals (unit weight times (2 times scale length in inches times frequency)^2) divided by 386.4. The 386.4 constant is gravitational acceleration in inches per second squared, which converts the result into pounds-force.

How is unit weight related to string gauge?

Unit weight is the mass per inch of the string. This tool estimates it from the wire diameter and steel density, but real wound strings differ slightly because of the core-to-wrap ratio. For exact figures use the manufacturer's published unit-weight tables.

Why does scale length change tension?

A longer scale length needs more tension to reach the same pitch because tension rises with the square of the vibrating length. That is why a baritone at 27 inches feels tighter than a 25.5-inch guitar at the same tuning.

What tension feels comfortable to play?

Most factory sets land between 13 and 18 lb per string, giving a total around 100-110 lb across six strings. Lower tension bends easily but can feel floppy in drop tunings; higher tension gives more attack and tuning stability.

Does this work for bass strings?

Yes, the physics is identical. Enter a longer scale (34 inches is standard for a 4-string bass), the heavier gauge, and the lower target pitch such as E1. Bass strings are wound, so treat the result as an estimate.

Guitar String Tension Calculator

This calculator finds the tension a single guitar or bass string carries when tuned to a chosen pitch on a given scale length. Tension is what determines how a string feels under the fingers and how stable it stays in tune, so knowing it helps you balance a custom set or move safely into a drop tuning.

How it works

String tension follows directly from the physics of a vibrating string. The fundamental frequency of a string is set by its length, its mass per unit length, and its tension. Rearranging that relationship for tension gives the standard luthier formula:

T (lb) = (UW × (2 × L × f)²) / 386.4

where UW is the unit weight in pounds per inch, L is the scale length in inches, f is the target frequency in hertz, and 386.4 is gravitational acceleration in inches per second squared (it converts the mass-based result into pounds-force).

The frequency f comes from the note. Each semitone multiplies frequency by the twelfth root of two, anchored to A4 = 440 Hz. The unit weight is estimated from the wire diameter and the density of steel, since a plain string is a solid cylinder of known cross-section.

Worked example

A plain 0.010 inch high-E string on a 25.5 inch Stratocaster tuned to E4 (329.63 Hz):

Cross-section radius is 0.005 inch, so the steel cross-section area is small and the unit weight works out to roughly 0.00002 lb/inch.
Plugging into the formula gives about 16 lb of tension, which matches D’Addario’s published figure for that string almost exactly.

Tips and notes

Wound strings (the lower three on a guitar, all four on a bass) carry their mass in a wrap wire around a thinner core, so this tool’s solid-cylinder estimate runs a little high for them. For mission-critical custom sets, cross-reference the manufacturer’s unit-weight table. The tension formula itself is exact; only the unit-weight estimate carries uncertainty. Everything runs locally in your browser.