Is a 20 watt speaker loud?

Could you please elaborate on the loudness of a 20 watt speaker? It's understandable that wattage is a measure of power, but how does it translate to the volume or loudness of the speaker? Is 20 watts considered loud for a home audio system, or is it more suitable for smaller spaces or personal use? Also, does the loudness vary depending on the type of speaker and its design? I'm curious to know how wattage affects the overall sound experience and whether it's a decisive factor in determining the loudness of a speaker.