The various estimation techniques and the steps involved in arriving at an estimate are described in Estimation Techniques. For a test plan, estimates can be made based on:

• Ratio figures
• Test object size
• Work Breakdown Structure (WBS)
• Proportionate estimation
• Test point analysis (TPA).

In order to increase the reliability of the estimate, you would be well advised to use your own figures based on experience as well as other means and techniques of estimating.