Work out crystal oscillator frequency instantly with clear inputs, formula shown and shareable results.
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.
Crystal pulling
df/f = (C1/2) x (1/(C0 + CL) - 1/(C0 + CLspec))
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.
More load capacitance pulls the frequency down. Less pulls it up, which is why an under-loaded crystal runs fast.