Guitar String Tension by Mass Calculator
Computes required tension in newtons on a guitar string for a given fundamental frequency from string length and linear mass density.
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Guitar string tension from linear mass: formula and example
Rearrange Mersenne's law to solve for T and you get T = 4 · L² · f² · μ. The result is in newtons as long as L is in m, f in Hz and μ in kg/m. Take a plain steel high E4 (f = 329.63 Hz) over L = 0.65 m with μ ≈ 0.0007 kg/m: that comes to T ≈ 124 N, about 12.6 kgf. A full steel-string acoustic set pulls roughly 80 kgf (~785 N) on the top, while a nylon classical set lands near 40 kgf (~390 N). That gap is why classical tops are thinner and rely on fan bracing.
Context and applications
Before switching gauges, luthiers work out the per-string tension so they don't warp the neck or split the top. Move from D'Addario EJ16 light (.012-.053, ~74 kgf total) to EJ17 medium (.013-.056, ~88 kgf total) and you add nearly 14 kgf, which is usually enough to call for a truss-rod tweak. Drop tunings like Drop D or D standard pull the tension down and feel slacker. Go up a gauge and the firmness comes back.
FAQ
Why does μ matter more than diameter? Wound strings (the bass ones) have a steel core wrapped in metal, so two strings can share a diameter and still differ a lot in mass. Go by the manufacturer's published unit weight rather than the gauge alone.
What is a safe tension for a classical guitar? Nylon sets come as normal (38-42 kgf), hard (42-46 kgf) or extra-hard (46-50 kgf). Push past 50 kgf and you risk lifting the bridge on an instrument that was built for nylon.
How does scale length change tension? T grows with L². So a 25.5" Fender tuned to E4 needs about 7% more tension than a 24.75" Gibson on the same gauge. It's the reason short-scale basses feel floppy.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.