Crystal load capacitance calculator
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Crystal network
Load capacitors
Required load capacitor
C1 = C2 = 2·(CL − Cs − Ct)
Nearest standard value
E12, closest to 20 pF
Actual load with standard pair
(C·C)/(C+C) + Cs = 11 pF
Deviation from target CL
How far the standard pair sits from the datasheet CL
About the model
The crystal manufacturer specifies CL for the load network C_load = (C1·C2)/(C1+C2) + Cs, where C1 and C2 are the two pin-to-ground load capacitors and Cs is the stray/PCB capacitance seen at each pin. Two equal caps are standard because each pin sees ground symmetrically. Using 2·(CL − Cs) per pin cancels the strays so the network lands on CL; a wrong load shifts the oscillation frequency by up to tens of ppm.
The nearest E12 capacitor may land slightly off target — the deviation row above shows how far. For tight ppm budgets pick the next standard value and fine-tune with a trimmer.
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