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Bass String Tension Calculator

Enter the string's unit weight, scale length and target frequency to find its tension.

Result

44.69 lb
20.27 kg

How it is calculated

The tool uses the vibrating-string relation in imperial units: T = UW × (2 × L × f)² / 386.4. UW is the string's unit weight in pounds per inch (from the maker's gauge chart), L is the scale length in inches, f is the pitch in hertz, and 386.4 is the gravitational constant in inches per second squared that turns mass into force. The result is tension in pounds, and the same value times 0.45359237 is shown in kilograms.

Here 2 × L × f is the wave speed along the string. Because the formula squares both scale length and frequency, doubling the pitch multiplies tension by four, and a shorter scale lowers tension a lot at the same pitch. All three inputs must be above zero. The calculation applies to the open string at the given pitch; it does not model fretted notes, string stiffness, or the string's stretch.

Worked example

Take a string with unit weight 0.0022 lb/in on a 34 inch scale, tuned to 41.2 Hz (the low E of a four-string bass). The wave speed term is 2 × 34 × 41.2 = 2,801.6. Squaring gives 7,848,963. Multiply by the unit weight: 7,848,963 × 0.0022 = 17,267.7. Divide by 386.4: 44.69 lb, which is 20.27 kg. The same string on a 30 inch scale would carry 34.79 lb, which shows how scale length changes feel.

Try this example →

Common mistakes

  • Entering the unit weight in grams per metre or ounces per foot. The field is pounds per inch, so a value copied from a metric chart will be wildly out and give a nonsense tension.
  • Typing the scale length in millimetres or centimetres. It is inches: a 34 inch bass is 34, not 864.
  • Using the wrong pitch for the string. A string tuned an octave higher takes four times the tension, so check the frequency for the actual note (41.2 Hz for low E, not 82.4).
  • Expecting the result to include everything that affects feel. Tension is only one factor; the stiffness of a thick wound string and the action also change how it plays.
  • Comparing sets by single-string tension. A balanced set is judged across all strings, so run the calculation for each one.

Sources

About this calculator

String tension is found from a standard string-physics formula: T = (UW × (2 × L × f)²) ÷ 386.4, where UW is the string's unit weight (mass per unit length, from the manufacturer's gauge data), L is scale length in inches, f is the target frequency in Hz, and 386.4 is the acceleration of gravity (g) in inches/sec² used to convert the result to pounds of tension.

Because tension depends on the square of both scale length and frequency, small changes in tuning or scale length shift string feel dramatically — which is why a 34-inch scale bass tuned to standard E-A-D-G feels noticeably different strung on a 30-inch short-scale instrument even with the same gauge strings. Bass players choosing string gauges, luthiers setting up instruments, and string manufacturers use tension calculations like this to match playing feel across different scale lengths, tunings, or drop-tuning setups.

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Comments (1)

  • Editorial team

    The squared frequency makes drop tuning easy to estimate. Taking a 34 inch scale and a unit weight of 0.0022, tuning the low string from E at 41.2 Hz down to D at 36.71 Hz lowers tension from about 44.7 lb to about 35.5 lb, roughly 20% less, which is why it feels floppier. What scale length and tuning are you working with?

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