The phrase "ascertain number" is correct and usable in written English.
It can be used when you want to determine or find out a specific quantity or figure.
Example: "Before proceeding with the project, we need to ascertain the number of participants who will be attending the event."
Alternatives: "determine the number" or "find out the number".
A researcher contacted schools to ascertain numbers of eligible participants.
While the number of cases of pandemic A/H1N1 in England was small, the Health Protection Agency ascertained numbers from laboratory testing of all known suspected cases.
Questions 10-12, answered by all respondents, asked whether they would like to return their PDA to the School in addition to ascertaining numbers of students with smartphones and feedback on future directions for the project.
Here we describe a more efficient modification of an already published method of locus specific copy number measurement for CCL3L1/CCL4L1 to ascertain copy number for a total of 1581 independent European samples.
It is only recently that a handful of studies in China have sought to provide some understanding of the issue by trying to ascertain the number of complaints in the studied hospitals or garnering patient feedback via questionnaires and interviews.
We use this to proxy desired family size which is asked in demographic surveys to ascertain the number of children that people want rather than the number they actually have.
It would be interesting to ascertain the number of people that have tried this drug or even better the number of 'hits' and compare it against the deaths as a result of this drug.
Managers can also ascertain the number, times, and nature of a worker's telephone calls, monitor e-mail, or track the number and nature of Web sites an employee accesses.
This court, it is respectfully suggested, will not undertake to ascertain the number of distilleries in operation, and to be placed in operation, in said collection district, and the number of storekeepers and gaugers to be placed on duty at such distilleries.
