# ELI5, why is the scale for how good something is x/5?

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Why do we measure things out of five? Like, 5 star hotels or restaurants? Why is it five and not, say, 37?

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Not everything uses this scale but it is quite common for internet reviews. I’d say it’s probably because it lines up well with these subjective values…

1 – poor

2 – fair

3 – neutral

4 – good

5 – excellent

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People are bad at math so small numbers are easy to understand. It also is like the A,B,C,D,F scale that people are used to in school. Also, most scales don’t go above 10 because you would reduce them, e.g. 10/20 is the same as 5/10. There is no point to higher numbers.

It’s not always. We have many different ranking systems. Movies are often rated out of 10. Gymnastics are rated with decimal point precision. YouTube rates things out of 2, like or dislike. You’re thinking of one rating system and thinking it’s the only one.

Why not 37 though? Because 37 isn’t good to divide by. What percentage of 37 is 22? Idk about 60. It’s hard to estimate if your scale is out of 37.

A couple reasons:

1. The vast majority of the world is comfortable with counting with 5s and 10s, because that matches the number of fingers on our hands. We intuitively grasp the value at a glance compared to some other arbitrary measure.

2. Five possible rankings offers an easy breakdown for what is being measured. 5 is perfect/near-perfect, 4 good, 3 average, 2 sub-par, and 1 terrible. Other numbers tend to lead to meaningless degrees of separation – what’s the difference between a 36 and a 37, for example?

It’s not always. Sometimes we rate things out of ten.

What we want from a rating is enough degrees to be able to distinguish things, but not so many that it’s hard to understand.

You want the worst things at one end, the best things at the other, and then a little middle ground for the average.

Let’s say we have the worst food, the middle food, and the best food. That’s at least three degrees needed. Now if we want to add in “above average but not the best” and “below average but not the worst” then we have 5 ratings levels (or “stars”).

We can add more degrees but that will inevitably make it harder for people to understand at face value the nuance between the tiers. The simpler it is, the more intuitive for someone glancing at a score, but the less accurately it might reflect the opinion of the rater.

We also tend to pick numbers which are intuitive to us, and us humans using base 10 tend to like things in 5’s and 10’s rather than 6’s and 12’s.