Rules of Thumb

Two black, stylized chevrons pointing to the right, often used as a fast-forward or "read more" icon.

Bandwidth of a signal: BW = 350/tr , where BW is the bandwidth in MHz and tr is the risetime in nanoseconds

Two thick, black chevrons pointing to the right, arranged one after the other.

10-90% risetime = 1.33 times the 20-80% risetime

Two thick, black chevrons pointing to the right, forming a fast-forward or double arrow symbol.

Wavelength at 100 MHz = 120 inches; at 1 GHz = 12 inches; at 5 GHz = 2.4 inches

Two black double-chevron arrows pointing to the right.

Speed of high-speed signals » 1 foot/nsec in air and 6 inches/nsec in FR-4

Two bold black arrows pointing to the right, stacked horizontally.

Therefore, a 1nsec risetime is 6 inches long in a PCB and 12 inches long in air