How Much Volts Is +4dBu?

To get this answer, we first find what 0dBm is, which is defined as 1mW into 600R for audio. P = VI and I = V/R so P = V^2/R. V = sqrt(PR) = 0.775Vrms. The ratio of +4dB = 10^(4/20) so +4dBu = 0.775 * 10^(4/20) = 1.228Vrms = 1.736Vpeak (the u in dBu means unterminated).