Differant Estimation Techniques

Here are some ways you can estimate the testing effort

-You could compare the project you are estimating to a completed project that is of similar size and complexity, then base your estimate on some percentage of the effort it took to test that previous project

-You could estimate the number of test cases (or function points) in the feature you are testing, then multiple that number times the average effort hours per test case (or function point) establish. The average effort hours are determine from metrics gathered from previous
test projects.

You could also base your estimate on number of requirements, using either of the above methods