How do you calculate watt usage on electronics?

veryconfused

New member
Well, Like a PSU for a computer says max it can go to is 400W, a TV has its own max wattage on off/on a light bulb is advertised as 60~120 depending on what you want, But how does that measure? is it 100W a minute, 100W an hour? Please clarify. Thank you.
 
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