Pendulum Period Calculator
Calculate the period and frequency of a simple pendulum from its length.
Mass does not appear, and that surprises people
A heavy bob and a light one on the same string swing at the same rate. Gravity pulls harder on the heavier bob but also has more inertia to move, and the two effects cancel exactly. What does matter is length: a grandfather clock's pendulum is close to 0.994 m because that gives a period of two seconds — one second per swing.
The small-angle assumption
This formula assumes swings under about 15°. Beyond that the period grows: at 45° it is roughly 4% longer than the formula predicts, which over a day is more than half an hour of clock error.
The formula
T = 2π · √(L / g)
Every result on this page comes from this formula. Nothing is rounded until the final display, so figures match a spreadsheet to the cent.
How to use the Pendulum Period Calculator
- Fill in each field with your own figures — the defaults are only there as an example.
- The result updates as you type, so there is no button to press.
- Check the breakdown under the main result for the supporting numbers.
- Use the copy button to take the result with you, or share the link to reload the same inputs.
Pendulum Period Calculator — frequently asked questions
Is this pendulum period calculator free to use?
Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.
How accurate is the result?
The maths is exact for the formula shown on the page. Accuracy in the real world depends on your inputs and on assumptions the formula cannot see, so treat the output as a well-grounded estimate rather than a quote.
Can I use it on my phone?
Yes. The page is responsive, weighs a few kilobytes and works offline once loaded, so it behaves the same on a phone as on a desktop.
What people search for
This page answers each of these searches. They are the exact phrases visitors use to find the pendulum period calculator.
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About this calculator
Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.
Last reviewed August 23, 2026 · Calculation runs client-side · No data collected · Report an error