Strictly speaking the capacitors should be chosen to match the load capacitance the crystal is cut for.
The equation for the load capacitance of a parallel resonant crystal is as shown below where CL is the effective load capacitance (which should match the crystal's specification), CL1 and CL2 are the values of the physical load capacitors, and CS is the stray capacitance of the circuit.
CL = (CL1 * CL2) / (CL1 + CL2) + CS
Usually, the two load capacitors are equal in nominal value so simplifying and solving for the physical load capacitor value gives
CL1 = CL2 = 2 * (CL - CS)
The stray capacitance for a well designed circuit board is likely to be 3-5 pF (perhaps a bit higher for a solderless breadboard) so for a crystal with a specified 30pF load capacitance, you'd select a pair of loading caps with a nominal capacitance of about 50pF. The closest commonly available value is 47pF but you might be able to find 51pF or even 50pF values.