jačina

1. (of sound, current, wind etc.) intensity; magnitude; volume
   Smanji malo jačinu zvuka, dete spava. — Turn the volume down a bit, the baby's asleep.
   Zemljotres jačine pet stepeni pogodio je Kraljevo. — An earthquake of magnitude five hit Kraljevo.
2. strength; power
   Ova rakija je velike jačine. — This rakija is very strong.
   Tim je pokazao pravu jačinu u drugom poluvremenu. — The team showed its real strength in the second half.

For "volume" the usual phrase is jačina zvuka.