Guitar String Tension Calculator
Calculate the tension in pounds for a guitar string based on scale length, gauge, target pitch, and material. Use it when setting up a new guitar, switching string gauges, or exploring alternate tunings.
Last updated: September 2026
Formula below · 2 sources (aes.org, Wikipedia) · Updated Sep 2026
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About this calculator
String tension is governed by the Mersenne–Young equation. This calculator implements the formula string makers publish: T = UW × (2 × L × f)² / 386.4, where T is tension in pounds, UW is the unit weight (pounds per inch of string), L is the scale length in inches, f is the pitch in Hz and 386.4 in/s² is gravity. The unit weight is estimated from the gauge d and the density ρ: UW = ρ × π × d² / 4, so T = π × ρ × d² × L² × f² / 386.4. Plain steel uses ρ = 0.284 lb/in³. Wound strings weigh less than a solid rod of the same outside diameter, so they use effective densities derived from published unit weights: nickel wound ≈ 0.235, phosphor bronze ≈ 0.265 and stainless wound ≈ 0.240 lb/in³. Tension rises with the square of the gauge, the scale length and the pitch. Optimal string tension for most electric guitars falls between 10–20 lbs per string; values outside this range indicate potential tuning instability or excessive neck stress.
How to use
Find the tension of a .010 plain steel string tuned to E4 (329.63 Hz) on a 25.5-inch Stratocaster scale. Set Scale Length to 25.5 and Target Pitch to 329.63, and pick Plain Steel. The calculator's gauge options start at .009; for a .010 string the arithmetic is: π × 0.284 × 0.010² × 25.5² × 329.63² / 386.4 = π × 0.284 × 0.0001 × 650.25 × 108,656 / 386.4 ≈ 16.3 lbs, matching the 16.2 lb D'Addario publishes for a PL010 at E4. With the .009 option the result is about 13.2 lbs.
Frequently asked questions
How does scale length affect guitar string tension and playability?
Scale length is the vibrating length of the string from nut to saddle, and tension increases with the square of that length. A longer scale — such as the 25.5-inch Fender standard versus the 24.75-inch Gibson standard — produces noticeably higher tension for the same gauge and tuning. This means longer-scale guitars feel stiffer and may require lighter gauge strings to achieve the same playability. Conversely, shorter-scale guitars (like 24-inch baritone conversions or parlor guitars) require heavier gauges to maintain adequate tension and intonation. Knowing exact tension figures lets you make data-driven decisions rather than trial-and-error gauge swaps.
What string gauge should I use when tuning a guitar down to drop D or lower tunings?
Dropping tuning lowers the target pitch frequency, which directly reduces string tension according to the squared pitch term in the formula. A standard .010 high-E string at E4 sits at about 16 lbs on a 25.5-inch scale; drop that string two semitones to D and tension falls by about 21% (to roughly 13 lbs), because tension scales with the square of the pitch. To restore comfortable playing tension in drop D or lower tunings, most players step up one or two gauge increments per string. For drop C or lower, dedicated heavy-gauge or baritone string sets are recommended. Running this calculator for each string at the target pitch lets you design a custom set that balances tension evenly across the neck.
Why does string material change the tension calculation for guitar strings?
Different materials have different linear mass densities — the mass per unit length of the string. Plain steel is relatively light, while nickel-wound and phosphor-bronze wound strings add mass from the wrap wire coiled around the core. Higher mass density requires more tension to vibrate at the same pitch over the same scale length, which is why wound strings feel stiffer than plain strings of the same nominal gauge. Because a wound string has gaps between its wraps, it weighs less than a solid rod of the same diameter; this calculator uses effective densities (plain steel 0.284, nickel wound ≈ 0.235, phosphor bronze ≈ 0.265, stainless wound ≈ 0.240 lb/in³) so tensions are comparable across string types when planning a mixed set.