Is a 20 watt amp loud enough?

I'm curious to know, for someone who's looking to purchase an amplifier, is a 20 watt amp loud enough to fill a small to medium-sized room with clear, distortion-free sound? Would it be suitable for practices, rehearsals, or even small gigs? Or would I need to consider a higher wattage model to ensure optimal sound quality and projection? It's important to me to make an informed decision, so any insight you can provide would be greatly appreciated.