Guitar String Tension Calculator

Guitar string tension determines how a string feels to play and how it affects your guitar’s neck. Understanding tension helps you choose the right string gauge for your playing style and instrument.

The Physics: String tension is governed by the vibrating string equation. For a string of a given length, tuned to a specific frequency, tension depends on the string’s mass per unit length.

The formula:

T = UW × (2 × L × f)² ÷ 386.09

Where:

• T = tension in pounds of force
• UW = unit weight, the string’s mass per inch of length, in pounds per inch
• L = scale length in inches
• f = the frequency you are tuning to, in Hz
• 386.09 = the acceleration of gravity in inches per second squared

That last divisor is the step everyone drops. Without it you have pounds of mass, not pounds of force, and every answer comes out about a third too small.

Unit weight comes from the geometry of the wire. Plain music wire has a density of 0.285 lb/in³, so a solid string of diameter d inches weighs:

UW = (π/4) × d² × 0.285

Put the two together and plain steel collapses to a single coefficient:

T = 0.00057976 × d² × (2 × L × f)²

A wound string is different. It is a thin steel core with nickel or bronze wrapped around it, and the winding has air gaps, so it weighs roughly 80% of what solid wire of the same outside diameter would. That is the factor the calculator applies when you select a wound string, and it reproduces the published tensions for wound sets to within a couple of percent.

Note what the squares mean in practice. Tension goes as the square of the gauge and the square of the frequency. Moving from a .009 to a .010 is only a thousandth of an inch, and it adds nearly a quarter to the pull.

Common scale lengths:

• 25.5 inches: Fender Stratocaster, Telecaster (standard “long scale”)
• 25 inches: Paul Reed Smith (PRS)
• 24.75 inches: Gibson Les Paul, SG, ES-335 (“short scale”)
• 24 inches: Some vintage Gibsons, short-scale bass guitars

Standard E tuning frequencies (Hz):

Tension on a 25.5" Strat, in standard tuning:

Every row above comes straight out of the calculator, and each sits within about 2% of the figure D’Addario publishes for the same string.

Most players find 14–20 lbs per string comfortable. Below 10 lbs the string flops and frets out; above 25 lbs it is hard work to bend and starts pulling the neck around.

A full .010–.046 set on a 25.5" scale totals roughly 100 lbs across the six strings. That is the load your truss rod is fighting, which is why changing gauge usually means a fresh setup: go up a set and the neck bows a little more, the action rises, and the intonation moves with it.