What does the phrase 'rule of thumb' mean?

What's the meaning of the phrase 'Rule of thumb'? A rule of thumb is a means of estimation made according to a rough and ready practical rule, not based on science or exact measurement. What's the origin of the phrase 'Rule of thumb'?

What is a rule of thumb for writing?

"Be specific" is a rule of thumb for most types of writing. "Look both ways before crossing the street" is a rule of thumb for pedestrians. If something is an official or written rule or law, it isn't a rule of thumb. Rules of thumb are unwritten but helpful guidelines. Everything, from parenting to architecture, has its rules of thumb.

What is a rule of thumb in finance?

A rule of thumb is an informal piece of practical advice providing simplified rules what apply in most situations. There are many rules of thumb in finance that give guidance on how much to save, how much to pay for a house, where to invest, and so on.

What is a rule of thumb for photography?

COMMON A rule of thumb is a general rule about something which is right in most cases. As a rule of thumb, drink a glass of water or pure fruit juice every hour you are travelling. A good rule of thumb for any type of studio photography is to use no more light sources than are strictly necessary.