I am trying to count all the numbers in a column that equal or exceed a
number that is entered manually in an individual cell (A1). But the countif
function does not work unless I enter the number directly into the formula.
For example:

Assume there is the number 5 in cell A1. I want to count how many cells in
range A4:A20 contain a number equal to or greater than the number in cell A1.
When I enter the following formula in Cell A21 it returns "0" even though
there are some cells in the column A4:A20 that contain a number equal to or
greater than 5.

The formula I enter in cell A21 is:

countif(A4:a20,"=A1")

This formula does not work unless I replace the cell reference "A1" with the
number I am using as the hurdle number - in this case the number is 5.

Is there some way to count the numbers in a column by making the count
function use a number in a defined cell as the hurdle number?