In most cases, local building codes will specify the maximum allowable space between railing pickets. In general, the maximum spacing for horizontal railings should be 4 inches, and the maximum spacing for vertical railings should be 6 inches. However, it is always important to consult the specific building codes for your area before installing a railing.
In addition to safety, the spacing of railing pickets can also affect the overall appearance of the railing. A railing with closely spaced pickets will appear more solid and substantial, while a railing with more widely spaced pickets will appear more delicate and airy.
Consider the style of your home and the desired aesthetic when choosing the spacing of your railing pickets.