I'd like to describe a person that he is a honest person and add how honest he is but couldn't figure out. How can I say this?
He is honest on the scale of 9 out of 10.
Is this correct? Or is there any shorter form that native speakers say?
I think a more likely construction would be:
I’d give him nine out of ten for honesty.
He is honest on the scale of 9 out of 10 is not fluent or idiomatic. If I had to express it with a scale, I would say something like
On a scale of one to ten, his honesty is a nine.
If you ranked honesty on a scale from one to ten, his would be a nine.
He's a nine on a one-to-ten scale of honesty.
But really, it sounds awkward and clumsy to rank someone's honesty on a numeric scale; I would rather say something like "He is almost completely honest" or "He is nearly always honest." That may be more of a stylistic issue than a linguistic one, though.
If you want short and pithy, you may have the wrong subject. If you want short, pithy and dynamic, you may also have the wrong verb.
His honesty is 9 out of 10.
Without further context, we can't tell whether this places his honesty at a 90% occurrence rate or puts him in the 90th percentile of his peer group, but that's hardly relevant. The one-to-ten rating scale is rarely used with precise measurements, and tends to represent nothing more than the strength of a gut-level reaction.
By the way, the scale isn't 9 out of 10. The scale is 1 to 10 (or sometimes 0 to 10), the rating is the 9 out of that range. Since it is a rating, we can use the verb "to rate":
His honesty rates 9 out of 10.
If you're not comfortable with the verb "to rate", the less formal "to get" serves the same function:
His honesty gets 9 out of 10.
The stative "is" implies that you don't expect the rating to change. Dynamic verbs like "rates" and "gets" imply that the rating could change over time. Perhaps is honesty rates a 9 this year, but next year his rating might drop to 3.
As a final note, the title of your question also works. I don't expect any native-speaking reader to be confused or mislead by
He's honest (9 out of 10).
where the parenthetical functions as an abbreviated afterthought or aside. I immediately interpreted it as "He's honest. ([I give/rate his honesty a] 9 out of [a 1 to] 10 [scale].)" Someone else might interpret it as "He is honest (9 [times] out of 10)", which is practically the same general sentiment, if somewhat less generous.
The simple parenthetical may be poor style in a formal context, but it looks fine from the perspective of an informal, conversational register.
An option that maybe doesn't have quite the same meaning, but is certainly more natural-sounding, is:
He is honest 90% of the time
Honesty is not about percentages. Honesty is about personal gain.
If he's honest most of the time, but lies about the critical things that, in the proper social context, he should not lie about, then the "90%" rating is meaningless.
Some things do not make sense to evaluate in terms of percentages.
i.e.: "Oh, I don't sleep with 99% of the women I meet, I only slept with that one."
I think honesty falls into this category.
There is no fluent way to describe what you're trying to describe, because honesty doesn't work that way. The concept itself is bizarre, so any description of it will be bizarre to begin with.
I'd like to also suggest the following:
He's a nine out of ten on the honesty scale.
This is idiomatic, and quite common in my experience.
Additionally, in my neck of the woods, we say something like this often enough:
On a scale from one to honest, he's a nine.
Since we so often rate things from 1 to 10, it's left implicit that the adjective ("honest") is the value of a score of 10. It's worth noting that this second construction is usually said with some sense of humour, since "a scale from one to honest" is, when taken literally, rather silly.
Someone who is perfectly honest, even to the point that it might actually sometimes be a problem rather than a virtue, is "honest to a fault". So in this case, we might say, "honest, though not to a fault".
This nine out of ten concept seems dodgy. If a retailer rips off 1 in 10 customers, I would simply call them dishonest, not "9 out of 10 honest". A reputation for honesty is very sensitive to fairly slight blemishes.
Isn't there a more simple way? Suggestions:
He is quite honest
He is rather honest
He is fairly honest
He is really honest
He is very honest
He is a [quite|rather|fairly|very|really] honest person
Rating on scales from 1 to 10 is so common that it has become idiomatic to say things like:
On a scale of 1 to perfectly honest, he’s a 9
where the 10 at the top of the scale is implied.
Examples of this construction:
He's more honest than 90% of people.
is the natural way to put it. The meaning is clear and it's a compliment.