The figure of merit of a logic family is given by the product of:

The figure of merit of a logic family is typically given by the product of its power dissipation (Pd) and propagation delay time (tp). This is often referred to as the power-delay product (PDP), and it's a key parameter in assessing the efficiency of a logic family.

Here are the steps to calculate it:

1. Determine the power dissipation (Pd) of the logic family. This is the amount of power that the logic family consumes when it's in operation. It's usually given in milliwatts (mW).

2. Determine the propagation delay time (tp) of the logic family. This is the amount of time it takes for a signal to travel from the input of a logic gate to its output. It's usually given in nanoseconds (ns).

3. Multiply the power dissipation (Pd) by the propagation delay time (tp) to get the power-delay product (PDP). The PDP gives you a measure of the energy efficiency of the logic family. The lower the PDP, the more energy efficient the logic family is.

So, the figure of merit of a logic family = Pd * tp.