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Simple Pendulum Calculator
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Free online simple pendulum calculator. Calculate pendulum period and frequency based on length and gravity, or reverse-calculate length and acceleration of gravity.
Select the quantity to calculate; the other two will be used as inputs.
Formula (Small Angle Approximation)
T = 2π × √(L / g)
L = (T / 2π)² × g
g = 4π² × L / T²
This formula applies to an ideal simple pendulum with small oscillation angles (typically < 15°), neglecting air resistance and string mass.

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In physics studies or experimental design, manually calculating the period of a simple pendulum can be tedious and prone to errors. This simple pendulum calculator can quickly determine the swing period and frequency based on the pendulum length and acceleration of gravity you input. It also supports reverse-calculating the length or gravity based on a known period. The period formula for a simple pendulum is T = 2π√(L/g), where T is the period, L is the length of the pendulum, and g is the acceleration of gravity.
This tool assumes a very small swing angle (typically less than 5°). If the angle is too large, the actual period will deviate from the calculated result. Input values must be positive numbers, and the pendulum length should not exceed millions of meters, otherwise the results may fall outside practical application ranges. All calculations are performed locally in your browser without uploading any data, ensuring your privacy.
The simple pendulum period formula T = 2π√(L/g) is only valid under the small-angle approximation. For large-angle swings, the period requires a series correction, though this is generally ignored in standard engineering calculations. If you need to use the results for a lab report, it is recommended to take multiple measurements and calculate the average. Additionally, you can use this tool to reverse-calculate the local acceleration of gravity: simply measure the period and length first, then select the "Calculate Acceleration of Gravity" mode.