How to find data with exactly 3 digits number

i have a column with several digits number. How can I find the cell with only 3 digits number?image description

And which of the numbers on the screenshot are “3 digits number”? the smallest number of digits I see in the selected column is 5 (63000). A conditional formatting with condition “greater than 99, and less than 1000, and is a whole number” would not highlight anything here.

That column contains 120000+ rows. I want to make sure that I don’t make a mistake for example to input let say “6000” as “600”

Ah, fine, then use the conditional formatting with the condition described above. I’d not ask, if you created a screenshot containing an example of what you want to highlight, instead of some numbers not presenting the property you are looking for. I wondered if you maybe somehow wanted e.g. to count non-0 digits, or something.

Use >Edit>Find and Replace... (Ctrl+H).
Enable Regular expressions.
If wanted enable Current selection only.
Select Values behind Search in:
Enter ^\d\d\d$ behind Find:
Find All

Explanation: The ^ and $ say “Nothing else!”
\dstands for any decimal digit. Instead of typing this three times, you can type \d{3}.
If you want to find numbers with up to three digits, you need to use \d{1,3}.

LibO has help,concerning RegEx. A very good tutorial about regular expressions is found here: Regular Expression Tutorial - Learn How to Use Regular Expressions.

[Edit1]
Concerning the additional information you gave:
Better use the standard filter for the respective column with Condition <= and Value 999.
(Also the filter supports RegEx if enabled.)

But: How will you find a typo creating a content of 9000 where 99000 or 90000 was correct?
You need to make sure that all the numbers are typed / imported / pasted correctly!
[Edit1]

Thanks for the answer… this is what I want. I finally find out how to do it same as yours…^\d{3}$…I’m such a noob in this…thank you so much.

Thank you for your suggestion. Typo error is also a concern. I guess that I really need to make sure that I type it correctly in the first place