Crystal Oscillator Frequency Calculator

Work out crystal oscillator frequency instantly with clear inputs, formula shown and shareable results.

About Crystal Oscillator Frequency Calculator

A crystal only runs at its marked frequency with the specified load capacitance. Deviating pulls the frequency by roughly (C1/2)(1/(C0+CL) - 1/(C0+CLspec)) in parts per million, which is why the wrong load capacitors are the most common cause of an oscillator being tens of ppm off.

Formula

Crystal pulling

df/f = (C1/2) x (1/(C0 + CL) - 1/(C0 + CLspec))

Worked example

With the default values below, Crystal Oscillator Frequency Calculator returns Actual frequency of 15.996952. Change any input above and every figure here is recalculated in your browser.

Inputs used

Nominal frequency: 16 MHz
Frequency tolerance: 30 ppm
Actual load capacitance: 18 pF
Specified load capacitance: 12 pF

Results

Actual frequency: 15.996952 MHz
Pulling error: -190.48 ppm
Tolerance band: 480 Hz
Total worst-case error: 220.48 ppm

Step by step

1Values used
2Crystal pulling
3Actual frequency= 15.996952 MHz
4Pulling error= -190.48 ppm
5Tolerance band= 480 Hz
6Total worst-case error= 220.48 ppm

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation or tax into account.
Figures are rounded for display to 6 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What load capacitors should I fit?

Choose them so the total load, including stray and pin capacitance, equals the crystal's specified CL. Stray capacitance of 3-5 pF per pin is typical.

Which way does extra load capacitance pull?

More load capacitance pulls the frequency down. Less pulls it up, which is why an under-loaded crystal runs fast.