Speakers don't normally deal in resistance, but impedence. A speaker's impedence is usually matched to the amplifier output . . . most computer speakers have a 4 ohm impedence. Impedence is the total opposition of the speaker's electrical circuitry (crossover net etc.) to alternating current (the amplified analog audio signal) that equals the square root of the sum of the squares of the resistance and REACTANCE of the circuit, usually expressed in ohms.
Reactance is another complex measurement, and I don't think it is doable by a multimeter. It is a function of capacitance and inductance in an electrical circuit.
I would just use the speaker manufacturer's specs. Just about all speakers are 4, 8, or 16 ohms.