I needed a simple crystal capacitor calculator, the formula used is: C = 2*Cload – 2*Cstray (taken from https://blog.adafruit.com/2012/01/24/choosing-the-right-crystal-and-caps-for-your-design/).
Just fill in C_load (from crystal datasheet) and C_stray (depends on PCB layout), then, press the calculate button.
CL: (from crystal datasheet)
CS: (from PCB layout)
C: (this is the capacitor to be connected to the crystal)
Optional: Make sure that CL and CL_Actual is not too far from each other.
Actual C_load if using the calculated value [CL = (C1 * C2) / (C1 + C2) + Cstray]
CL_Actual: